SACRED TRUTHS 2024Save 20% on Registration Through November 30th

What Is Christology? Dr. Steve Duby

Phoenix Seminary
February 9, 2022


Dr. Arnold interviews Dr. Duby on the subject of Christology.

Topics of conversation include:

  • What are God’s incommunicable attributes?
  • God’s aseity, and why it matters for Christology
  • The importance of Philippians 2 in understanding Christology
  • God’s immutability as it relates to the incarnation
  • The mystery of Jesus’s humanity and divine power
  • Resources for further reading on Christology

Dr. Steve Duby serves as associate professor of Theology at Phoenix Seminary. He holds a Ph.D. in Systematic Theology from the University of St. Andrews, and is the author of several books, including Divine Simplicity: A Dogmatic Account (T&T Clark, 2015), God In Himself: Scripture, Metaphysics, and the Task of Christian Theology (IVP Academic, 2019), and soon to be released, Jesus and the God of Classical Theism (Baker Academic, 2022).


Subscribe on:

Apple Podcasts



Intro (00:00):

Welcome to Faith Seeking Understanding, a podcast from Phoenix Seminary—helping Christians grow in their understanding of the faith, hosted by Dr. Brian Arnold, president of Phoenix Seminary.


Brian Arnold (00:16):

There are many mysteries in the Christian faith. How did evil enter the world? How does divine sovereignty and human freedom work? How can God be one and three? But to me, the grandest mystery is that God could become man. What does it mean that Jesus Christ is fully God and fully man? How does this work? It is a profound mystery, but it is the very cornerstone of the Christian faith. Particularly, we want to focus today on what it means that Jesus was God. Not many people today doubt that Jesus was a man. Basic historical record confirms that Jesus of Nazareth was a man who lived 2000 years ago. However, to say that he is God is another thing altogether. Well, to help us understand Christology, we have theologian Dr. Steve Duby with us today. Dr. Duby is associate professor of Theology with us at Phoenix Seminary. And he's written several books, including Divine Simplicity and God in Himself. And he has a book coming out soon titled Jesus and the God of Classical Theism. Dr. Duby, welcome to the podcast.


Steve Duby (01:11):

Thanks for having me.


Brian Arnold (01:12):

So we always ask our guests the big question, today that question is—what is Christology? But I thought first you might tell us what even attracted you to this topic?


Steve Duby (01:21):

Yeah, well the easy answer is I'm a Christian, so I care about Jesus. Jesus matters. But of course going a little bit beyond that, I have spent some time trying to study God's attributes, trying to study the doctrine of the Trinity. And inevitably, when you deal with those questions, you start thinking about how the person of Christ fits into all of that. How do earlier teachings from the church, that you can find in a place like the Nicene Creed, how do those fit together with the way that Jesus is described in the gospels? So it was a natural thing for me to pursue that question. And in particular, to think about how Jesus is the highest revelation of God, and yet he lives a human life. He undergoes change, he suffers—how does that fit together with an earlier Christian account of God, according to which, God doesn't change, God transcends time, and so forth? So those kinds of things have gotten me interested in studying this topic further.


Brian Arnold (02:18):

And honestly, it's something that a lot of Christians have probably not thought much about. And even in the academy, it's not been dealt with a ton—to say, what does it mean for Jesus to be fully God? And looking at that through the lens of classical theism, looking at that...particularly one of the things you have focused on are God's incommunicable attributes. And if that's true of who God is in his essence, then it must be true of Jesus, for him to have the essence of divinity. So maybe define for us really quick, what we even mean by incommunicable attributes.


Steve Duby (02:47):

Yeah. Those are attributes of God that are often most challenging for us to reflect on. Those are the ones that are not shared by us creatures. That's what incommunicable means. Not shareable. There's a sense in which we're not exactly like God, even when it comes to attributes that we do share, like wisdom and goodness. We don't have those in an infinite way as God alone does. But there are certain attributes of God that are not shared by us in any respect, among which would be independence, or aseity. God has life in and of himself, from no one else. Well, he's the only one that has that. And those attributes—they're challenging for us to study. And they also raise some serious questions about how it all connects to Jesus. Because as I said, he's the highest revelation of God, and yet living this ordinary humble human life that's filled with change, that's located in time, that involves suffering, and so forth.


Brian Arnold (03:41):

Well, let's spend some time—because I'm sure you do this a lot in your book—diving into some of those particular words you just used, which are foreign to many people today. Like God's aseity. So what does that mean of the triune God, and then, particularly, what does that mean of Jesus? And why does that matter for Christology?


Steve Duby (03:58):

Yeah, that's a great question.


Brian Arnold (03:59):

Thank you.


Steve Duby (04:00):

Yeah. Well, I like complimenting questions. It's very important. Aseity, it is an unfamiliar word, but it just comes from the Latin phrase a se, meaning "of himself." And so when we say aseity, we're just trying to signify that God has life in and of himself. He doesn't depend on anybody else, or anything else, to be the God that he is. That's true of the Father, Son, and Spirit. They share that divine attribute. And it's also, we have to say, true of Jesus all throughout his incarnate life and ministry. He didn't get rid of that when he took on flesh. And among other things, that means that he didn't stop being capable of being the Savior that we needed him to be. When we read a passage like Philippians two, for example, where Jesus emptied himself, Paul doesn't specify anything of which Jesus emptied himself, or anything that he got rid of. He just says "he emptied himself by taking the form of a servant." So an attribute of God like aseity continues to be true of Jesus. And that's important, because we need him not to stop being God when he comes to us to reveal God, and to make atonement, and be our Savior—with all that that encompasses.


Brian Arnold (05:11):

Well, one of the things that has happened in the course of church history, is a lot of heresies have come in, which are things that are not true of the Christian faith. Many of these deal with the person of the Son. So somebody like Arius, who said "there was a time when the Son was not." And then that sparks the Nicene Creed, and a lot of theologians are writing on this in the fourth century, and then on. And then we see a resurrection of this, really, in our modern day with people like Jehovah's witnesses, who are like modern day Arians. And that's why it's important for us to know these things. And you just touched on another one, which is what we call kenosis—that the Son empties himself. And I think a lot of people, even in our evangelical churches, would read something like Philippians two and say—Jesus had to get rid of his divinity. Part of his humility is getting rid of divinity. But then he is not God anymore. So how would you walk through somebody in your church who would even say—okay, what does it mean that Jesus let go of his divinity? And you would say—well, let's stop there, because that's not how we think about that. So walk us through maybe even Philippians two. Because I think it's important for us to use that as a point of intersection for who Jesus is, especially as God


Steve Duby (06:16):

It's a crucial passage for the Christian life, and for our Christology, of course. In Philippians two, Paul is pointing out Christ as the chief example of humility that we have to imitate in the Christian life. And then, in order to spell all of that out, he starts talking about how the Son of God humbled himself, took on human flesh. In verse verses six through 11, I should say, Paul goes on to speak about how Christ is in the form of God, but he emptied himself, taking the form of a servant, being made in the likeness of human beings. And as I said before, one important thing there is that when Paul says Christ "emptied himself," he doesn't go on to specify something of which Christ emptied himself. So this is not an emptying by subtraction. It's not an emptying by getting rid of something.


Steve Duby (07:06):

It's actually an emptying by addition, which might sound funny, except all that that means is—Jesus not only was still God, but also took upon himself something that was below God. He took upon himself our lowly human nature. And as he lived on earth—and of course he still lives in heaven in a human nature—as he did that, he didn't set aside his divinity. It's tempting to go there, but on a closer look at the passage, he continues to be God. And then in his human nature, he humbles himself by becoming obedient to the point of death. That passage, that hymn, if that's what it is, a song sung by early Christians, it ends with Jesus being exalted. Which might raise questions about how he gets something from that, if he still was God the whole way through. But he's exalted in the sense that his divine glory was manifested, and he's exalted in his human nature, of course, in that he receives the immortal resurrection body that we all are looking forward to. It's a great passage, pivotal for Christology, and such a wonderful example for our Christian life.


Brian Arnold (08:14):

One of the illustrations I've heard used for that, and I'll keep this theologian nameless, in case you blow up the illustration. But he said—imagine, you know, here we are in Phoenix, lots of Tesla dealerships. And imagine you get this nice Tesla, and you take it out for a test drive, and you run it through the desert on a rainy day that happens twice a year. And this thing gets covered with mud. That might help explain what we mean by, you know, he empties himself by addition. In that you come back, and you've got this car caked with mud, but underneath is still the pristine Tesla. I mean all analogies break down, but is that kind of what you even mean by "emptying by addition?"


Steve Duby (08:56):

I can see the connection there. The Tesla has not lost its Tesla-ness, if we can create an English word. Yeah. So throughout his earthly life, there is...or as Jesus begins his earthly life, we might say, there is an emptying that involves taking on a human nature. And we can add, there is also, usually, a concealing of his divinity throughout that time. There are times when his uniqueness, his divine glory breaks through, or peaks through, for example on the Mount of Transfiguration. But for the most part, what was seen was a human person living in ordinary human ways. And then, of course, his divine glory is manifested in a special way when he is exalted. So I've never thought about Tesla in that way, but I suppose...


Brian Arnold (09:46):

But now you will.


Steve Duby (09:47):

Now I will.


Brian Arnold (09:49):

So let me ask you about another one. And you kind of opened the door for this earlier, and that is God's immutability. God does not change. In fact, one of the ways we know God is God, is that he doesn't change like a man changes.


Steve Duby (09:59):



Brian Arnold (10:00):

So, but then with the incarnation, you have God taking on human flesh. And so a question that I get, every time I teach Christology, from a student who's alert and thinking is—does that mean that God changes? Especially because one of the things we say about Jesus in his—we'll call it the hypostatic union, I'll let Dr. Duby define that for us here in a little bit—is that Jesus not only took on flesh for us, but that he'll be embodied forever.


Steve Duby (10:33):



Brian Arnold (10:34):

Where he wasn't before the incarnation. So has that emitted some change In Jesus?


Steve Duby (10:41):

That's a great question. I think it's important to recognize that in the hypostatic union—so I'm going to use that phrase, since you've invited—


Brian Arnold (10:48):

Go ahead and define it.


Steve Duby (10:50):

It's...that is just referring to the union of Christ, two natures in one person. The union of his deity and his humanity in the one person of Christ. And in the hypostatic union, it's important to remember that Jesus's divinity does not get switched over to his human nature. There is no confusing of the two natures. So, in light of that, we can talk about Christ in more than one way. We can say that in his unchanged divine nature, he continues to be the unchanging God. His divinity is distinct from his humanity. So there is a meaningful way in which we can say he continues to remain unchanging and unchangeable.


Steve Duby (11:31):

We would only get into trouble there if we assumed that the divinity of Jesus and the changeable humanity of Jesus somehow had to blended together. Then you would have trouble saying that he remains unchangeable as God. But the two natures remain distinct in the one person of Christ. So we say a number of things about Jesus that are applicable to him with regard to his divine nature, and a number of other things that we say about him that are applicable to him with regard to his human nature. Which I think leads to some unusual statements that we make about Jesus, and that even the Bible makes about Jesus. One thing I often like talking with students about is how Paul in Acts 20:28 says that God put these Ephesian elders that he's talking to, over the church. Overseers of the church of God, which he bought with his own blood.


Steve Duby (12:22):

So apparently for Paul, and for Luke who records this, you can say—God has blood. But the key there, is we're talking about the person of Christ, who is both divine and human. So the meaning is—this person, who is God, who also has a human nature, has blood, with regard to his human nature, that he shed for our forgiveness. And there are other things that we can say, in talking about the person of Christ, that might sound strange at first, but can be clarified on further inspection. So you said something along the lines of—is it okay to say that God changes? Well, if we're talking about God as God, with regard to his divine nature, no, he doesn't change. But if we're talking about...if by God we mean this person of God the Son, who is truly God, but is also truly human, if he...if the question is—does God change with regard to the human nature that God the Son assumed, then yeah, you can say God changes.


Steve Duby (13:20):

Just as you can say—God suffered, God poured out his blood for the church. We're in a unique situation when we're talking about the person of Christ. So we have to be nimble and alert to how language works. And it's actually exciting to be able to speak clearly about this and understand what it means. I think it's theologically exciting, but also spiritually edifying in some ways.


Brian Arnold (13:43):

Well, in a lot of ways, right? And it's like you said—not confusing the nature. So I'd mentioned Arius before—"there was a time when the Son was not." So the Nicene Creed happens. But then that sparks a lot of Christological debates in the fourth and fifth centuries. And it leads to what we call the Chalcedonian Definition in 451, where they're really having to narrow in the focus—what does it mean for Jesus Christ to exist in one person with two natures? And one of the errors that's made, and I think you were alluding to it earlier, is—and we're just going to douse you with theological terms right now—is eutychianism, or monophysitism, which is this idea that the two natures blend into one new nature, and so you can almost illustration that I've used, which again, you might blow up, is, you know, like a Gatorade powder into water, that kind have this powder, you have the water, but it kind of blends and mixes into one new substance. But that's not what the church fathers saw Scripture teaching. That we really need to keep these two natures not confused, not intermingling, but we can say that God does not change. The divine nature never emits change, but the human nature does. Now, as we talk about things like the suffering on the cross...or maybe even walk us through the passion narrative, from the garden where Jesus says, "not my will but your will be done," into what it means for God to suffer on the cross.


Steve Duby (15:08):

Yeah. That's a big question. I've identified your questions as great questions. Now this one is's a big question. So I suppose it's great too. But in Gethsemane, we have Jesus, of course, as you said, praying to the Father—not my will, but yours be done. That is a glimpse into the fact that Jesus has, not only a divine will, but also a human will. And in that human will, to put it simply, he was not looking forward to the cross. He really despised the pain that he was about to experience. So in his natural human will, he expressed to the Father the fact that he didn't like the thought of what was about to happen. But of course, in Christ's case, he never allowed any of that to deflect him, to turn him away from doing what the plan of God had set forth.


Steve Duby (15:52):

So he was still determined to go to the cross. In that regard, he says to the Father that he wants the Father's will to be done. Interestingly, because the Father, Son, and Spirit all share the divine will, that means he wanted his own divine will to be done. We may not see that just from that passage, but thinking with the whole of Scripture we have to say that as well. Of course there are other things that happen in the run up to the cross. There is the arrest, the trial, and so forth. But then, when we come to the cross, we see Jesus...we see the pinnacle of Jesus's suffering on earth. And there are questions that come up there about whether the Father also was suffering in some way in that moment. And then there are questions about whether Jesus, not only in his humanity, but perhaps also in his divinity, was undergoing suffering on the cross.


Steve Duby (16:41):

Historically Christians have said—no, the Father was not suffering in this moment. And they've also said—no, Jesus wasn't suffering in his divinity, but only in his humanity at that moment. Now I think the question that comes up for us, as we hear those things today, is—doesn't that make the Father sound cold or cold-hearted? Doesn't that make Jesus sound inappropriately invincible, or something like that? Like the Terminator, who cannot really relate to human pain? Although I've never seen The Terminator, if I'm allowed to say that. So I don't know if the Terminator could relate to human pain or not.


Brian Arnold (17:12):

I don't think so.


Steve Duby (17:13):

Okay. Fair enough. So we're good to go. With regard to the Father not suffering, he doesn't have a human nature, which means that even as he loves, even as he cares deeply for creatures, and for his own perfect Son, he is not subject to being harmed by the evil, or by the bad things that are happening in the world.


Steve Duby (17:34):

That's at the heart of what we mean when we use the attribute impassibility. It doesn't mean God doesn't care. It means that God is not subject to being harmed, or losing his own wellbeing. So the Father was impassible, and also the Son, in his divinity, was impassible. In his divinity, Jesus just could not be deprived of his own wellbeing, his own fulfillment, his own stability, as God. That doesn't make God cold-hearted, that's actually good news for us. We need the God who cannot be defeated by evil, who cannot be brought down by evil, to deliver us from our evil and suffering. That is vital. And that's a comfort to us in the Christian life. And the Lord has been so gracious that we also get the other side of this, where the divine person that we needed to come and save us, he has come to save us, and in his human nature has experienced true human suffering.


Steve Duby (18:28):

It's not a combo of divine and human suffering that we might not be able to relate to. That might not quite make him our sympathetic High Priest. But in fact, the suffering that Jesus has undergone is pure, unalloyed human suffering on the cross. In which, of course, he bore the penalty of our sins, but also in which he was equipped to be the sympathetic high priest that the book of Hebrews talks about in chapter two. So in Christian theology we have a God who is unable to be conquered by evil, unable to be distressed or overwhelmed by evil, and also a God who took on flesh to suffer for us and to experience firsthand what it is to undergo suffering in the trials of human life.


Brian Arnold (19:11):

It's the beauty of the Christian message. It's unparalleled of anything else—that an infinite God, who cannot experience evil, or cannot be taken out by evil, right? Taking on human flesh for us. It is remarkable what our God has done for the salvation of people, and it should always lead to doxology. I think that's important for our listeners to hear. This is not just about talking about esoteric terms that theologians toss around. This is infinitely important for our lives and our eternity—to know this God and to love him, because we've been loved by him.


Steve Duby (19:49):



Brian Arnold (19:50):

So how does this play out? So we talked about the cross. I want to now talk about the incarnation. I want to talk about the manger in Bethlehem. And I think it was Cyril of Alexandria, but I could be wrong, talking about how "he upholds the heavens from the manger." So how is that happening? How is baby Jesus upholding the universe by the word of his power?


Steve Duby (20:12):

Well, you're using the word "how," and that's a question that we are always drawn to. I'm tempted to say—I don't know how, but I do know that I need to say that it happens. That it is the case. And yet, in our human existence, and in our theology, we always want to get into the question of how a little bit. How does that actually take place? I think we're limited in our knowledge of the how at this point, but we can say some things. I would also, among other things, I would point back to the distinction between Christ's nature, two natures. He remains God, even as he has assumed human flesh, in which he starts out as a baby. So by his unchanged divinity he is still exercising divine power, including upholding the entire universe by the word of his power, Hebrews 1:3. And at the same time, this one person now exists in a human nature, and in that human nature is subject to the limitations that it involves, including limitations pertaining to normal human development. So yes, he doesn't have the strength even of a full-grown man when he is newly born. And yet with regard to his divine nature, divine power, together with the Father and Spirit, he's upholding the heavens and the earth. I still don't know that I'm penetrating into the question of how...


Brian Arnold (21:36):

Nope. Sure aren't, no, but that was beautiful.


Steve Duby (21:38):

So that's actually a lesson in Christian theology here, I think. We cannot always comprehend the how, but we can do something, there. We can get to it a little bit. And then also we can at least reinforce that we're not slipping into logical contradictions here. I think the attack on the faith would be—you're talking nonsense, one person can't do both of these things. I can say—actually, we don't have a logical contradiction. But that still doesn't mean I've fully comprehended the mystery, as God himself alone will do.


Brian Arnold (22:08):

Alone will do. Even in eternity future, we will not have access into all knowledge, because then we'd be God. And we are not God. So there's going to be things behind the veil of mystery that the Bible talks about in Deuteronomy 29:29—even there are secret things that belong to the Lord, and only to the Lord, that we won't know. So I was mostly just joking with you, because I agree with you—we need to have some epistemic humility in recognizing things we cannot know. And yet, you know, theologians have talked about the ability for Jesus, in his divine nature, that cannot be held just to this little baby in a manger.


Steve Duby (22:44):



Brian Arnold (22:45):

Right? I mean, part of him having omnipresence that doesn't go away, omniscience that doesn't go away just because he's a baby in a manger. And I know theologians have at times referred to this as the extra Calvinisticum, and attribute it to Calvin, but Athanasius certainly talks about this as well in his book On the Incarnation in the fourth century.


Steve Duby (23:06):

So you've introduced the Latin phrase here. Not...I haven't. I'm just cleaning up the mess, that's all.


Brian Arnold (23:12):

Absolutely. But I think it's fine to even just stop there and say—that's as far as we can really go into some of these mysteries. Maybe a bit further, but you probably do that in your book.


Steve Duby (23:21):

Yes. Yes. Do we need to talk about the extra Calvinisticum?


Brian Arnold (23:24):

No, I don't think so. I think we need to leave people longing for more, and going out to get your book. When does that actually release?


Steve Duby (23:31):

It is supposed to come out in June with Baker Academic, and they have two other books coming out at the same time on related things—on the person of Christ and Christology. And I hope all three of them complement each other.


Brian Arnold (23:44):

And I want to remind everybody—it's Jesus and the God of Classical Theism. I will say, I mean, one of the things I appreciate about Dr Duby is he is accessible, but he's going to make you work too, because you're dealing with the things of God and that requires a certain level of reflection. So I encourage you to get out there and read it. But I also want to see if you can recommend a couple resources that are for the theological novice, just beginning to wade into some of these issues. What have you found to be the most helpful?


Steve Duby (24:12):

Well, one book that that would be accessible here would be The Person of Christ. It's in a series of books that introduce major theological topics. That one is by Steven Wellum. And he's got a bigger book on this as well, God the Son Incarnate, published by Crossway. So those are a couple of starting points. Another option would be to pick up a big theology book that you've found trustworthy on many topics, and dive in there on the person of Christ. So it's usually a topic treated in your average systematic theology book.


Brian Arnold (24:48):

Absolutely. Well, Dr. Duby, I'm so grateful that you joined us today. And what I hope this does for everyone, more than anything else, I hope we we've grown your knowledge of God, but more that we've grown your love for God. That the God of the universe would take on human flesh for us and our sinfulness, and give us a way to be reconciled back to himself—that is love that is profound. So thank you for leading us into that today.


Steve Duby (25:09):

Thanks for having me.


Outro (25:11):

Thank you for listening to the Faith Seeking Understanding podcast. If you want to grow more in your understanding of the faith, consider studying at Phoenix Seminary, where men and women are trained for Christ-centered ministry for the building up of healthy churches in Phoenix and throughout the world. Learn more at


© 2023 Phoenix Seminary. All Rights Reserved