This will be a brief review of the second 2014 debate on the "Unbelievable?" radio show between Simon Gathercole and Bart Ehrman on the topic of Christology, specifically a discussion of the earliest texts in the New Testament such as Romans 1.3-4 and Philippians 2.5-11. The discussion was sparked by the publication of Ehrman's How Jesus Became God and a response volume to which Gathercole contributed titled How God Became Jesus. Timestamps refer to the recording here; note that the timestamps might vary depending on how your browser loads the recording and other factors. The debate starts after the third minute, moderated by Justin Brierley.
In his initial comments, Ehrman says that this issue (who Jesus was) is "fundamentally important for everybody, whether they're a Christian or not a Christian." (4:55). This is a good take. Despite Ehrman's dubious conclusions on the historical Jesus, this remark is a refreshing point of agreement.
Clarifying his views on the evolution of early Christology, Ehrman goes on to say that "Christians didn't come out and call Jesus God for decades after his resurrection." (6:50) Later, he comments about how he changed his mind on the subject of Jesus' burial, saying that the traditions of Jesus having a tomb that was discovered empty are "probably not historical" (8:20). This was not the subject of the debate, so I will not be discussing it here. Those interested in a response to arguments from Ehrman and others concerning the historicity of Jesus' burial can consult this post from jobapologetics or this video from InspiringPhilosophy. Both links cite a plethora of scholarly sources for further research on the topic.
At the 12 minute mark, Ehrman summarizes the consensus dating of the Gospels, placing Mark around 65 or 70. Gathercole agrees with the chronology fleshed out by Ehrman. I don't think the evidence for these dates is strong enough to command the consensus they enjoy, but this is irrelevant to the topic of the debate so I will not discuss it here. I will post a review soon of Jonathan Bernier's new book on the topic.
The discussion of early Christology begins in earnest at 14:18, when Brierley introduces Philippians 2 as a purported example of early high Christology. For reference, here is the text from the NASB:
5 Have this attitude in yourselves which was also in Christ Jesus,
6 who, as He already existed in the form of God, did not consider equality with God something to be grasped,
7 but emptied Himself by taking the form of a bond-servant and being born in the likeness of men.
8 And being found in appearance as a man, He humbled Himself by becoming obedient to the point of death: death on a cross.
9 For this reason also God highly exalted Him, and bestowed on Him the name which is above every name,
10 so that at the name of Jesus every knee will bow, of those who are in heaven and on earth and under the earth,
11 and that every tongue will confess that Jesus Christ is Lord, to the glory of God the Father.
This passage is regarded by some scholars to be pre-Pauline. At 18:00 Gathercole answers a question about how this conclusion is reached. He emphasizes the unusual vocabulary as one factor, though he qualifies that by saying that the difficulty with this approach is that the corpus of Paul's letters is tiny. This is generally a good principle: while unusual vocabulary is some evidence for non-Pauline origin, since the corpus is sufficiently large to get an idea of Paul's verbal and grammatical inclinations, writers use unusual vocabulary frequently so caution is warranted.
Returning to around the 16 minute mark, the conversation turns to various translation-related issues in the first section of the poem. Both Gathercole and Ehrman think that translating the first part of verse 6 as "being in very nature God" is dubious. Gathercole says that the more controversial part is "over the grasping bit" (17:00). Gathercole notes that translating it as "grasped" suggests that Jesus didn't already have equality with God, but the alternative translation of "exploited" suggests that he did have it but didn't abuse it. At 17:40 Ehrman comments that the word for "grasped" (harpagmos, from arpazō) isn't used very much. Indeed, this is the only occurrence of this verb in the New Testament. Due in part to time constraints, neither scholar lays out a case for preferring one translation over the other.
At 18:50, Ehrman summarizes his interpretation of the Christology of this creed as "Before Jesus became a human, he was a divine being with God in heaven, but he didn't want to seek equality with God... Then, God exalts him more highly than he was before." At 19:40, Ehrman notes that the language of every knee bowing and every tongue confessing is a quotation from Isaiah applied exclusively to YHWH. Thus, he argues, Jesus became equal with God after the resurrection.
At 19:33 Gathercole explains his interpretation of the Philippians passage. He notes that his primary disagreement is over the translation of harpagmos; he finds it convincing that this should be translated as saying that Jesus had equality with God but didn't want to hold onto it. He then comments as to the difficulty of treating a small hymn like this in isolation and suggests going elsewhere in Paul to find his high Christology. Specifically, he cites 1 Corinthians 8.6: "yet for us there is only one God, the Father, from whom are all things, and we exist for Him; and one Lord, Jesus Christ, by whom are all things, and we exist through Him."
Seeing as the primary difference between these two interpretations of the Philippians passage depends on the translation of harpagmos, some comments about this are in order. Scholars have long debated the meaning of this word and the matters of syntax are complex. For those interested in reading more about this term, perhaps the best place to start is Roy Hoover's 1971 landmark study.  On the basis of his survey of other uses of the word, Hoover suggested a translation of Philippians 2.6 as "he did not regard being equal with God as something to take advantage of". This went without serious challenge until 1988, when J. C. O'Neill published a brief critique of Hoover's conclusions, arguing that harpagmos is best understood as robbery.  Gordon Fee took issue with O'Neill's critique, saying "by turning Hoover's findings into a 'rule', O'Neill eliminates the 'rule' by noting the exceptions. But that is not the same thing as eliminating Hoover's understanding of the idiom."  Most recently, Michael Wade Martin published a rebuttal to O'Neill's comments and proposed some refinements to Hoover's thesis.  Martin's primary conclusion is that the use of harpagmos itself is ambiguous and its meaning should be settled by context. This latter position seems safest. I think the context provides a strong case for the equality of Jesus with God by 1) the wording "in the form (morphē) of God" and 2) the theological impracticality of translating harpagmos as "robbed". These considerations are not conclusive, though, so Pauline Christology should not be settled on the basis of this text alone.
There is little to comment on from the 30 minute mark to the 40 minute mark. Ehrman and Gathercole primarily discuss the divisions between creator and created in first-century Judaism, where they generally agree. Gathercole's central contention is that the worship of which Paul declares Jesus worthy would be unfitting for a created being: "If Jesus is a creature, then you jolly well shouldn't worship him." This conclusion comes from passages like Romans 1 ("worshiped and served the creation rather than the Creator"). Thus, Paul viewed Jesus as uncreated.
At 39:30, Gathercole explains that a central problem with an exaltation or adoptionist Christology is that it would make a creature into a non-creature. Ehrman responds by saying that Jesus is still a creature, but now one who has been exalted to the level of God. He uses the analogy of a Roman emperor adopting a son. Further, Ehrman comments that Paul's condemnation in Romans 1 is irrelevant because 1) Paul is talking about worshiping idols, and 2) Jesus has now been exalted to the level of God, an uncreated thing. Later, Gathercole responds to 1) by agreeing that Paul is indeed condemning a specific brand of idolatry, but in doing so he reflects his belief that only the creator is worthy of worship.
This is an interesting contention from Ehrman. One objection is that it's difficult to view a created Jesus as being equal to God, because the creature/creator distinction precludes any notion of metaphysical equality—the creator will always be greater than the creation.
Ehrman goes on to defend his view that Paul viewed Christ as a created being by saying that "from whom are all things" in 1 Corinthians 8.6 includes Christ. Gathercole references the second part of the verse saying that "through [Christ] are all things". Here I think he drops a good rebuttal. If Ehrman wants to argue that "from [God] are all things" necessarily implies that Christ is a created being (interpreting the "all" literally), then saying that "through [Christ] are all things" would imply that God exists through Christ. I doubt this is a position Ehrman would want to affirm, given his belief that Paul viewed Christ as a created being. Further, if God's existence depends on Christ, it would suggest that Christ is higher than God in some way. Thus, Ehrman would have to concede that God is excluded from the "all" in the phrase "through [Christ] are all things". This significantly weakens his argument that "from [God] are all things" necessarily includes Christ—if the second phrase permits an exception, the first one can as well.
At 44:00 begins the discussion of the "tunnel period". This is the period of about 20 years from Jesus' death to our first Pauline letter. Ehrman says that the best way to figure out what was going on Christologically during the tunnel period is to look at pre-Pauline creeds and hymns in the letters of Paul. While this is probably our best bet for elucidating early Christological beliefs, I don't think it can yield much certainty. Creeds are often condensed, for one thing, and leave out a lot of qualifications that might impact our interpretation. Another concern is that Paul is widely argued to have redacted Christologically inadequate creeds to make them compatible with his own Christology, but the speculation employed to reconstruct the original protocreeds is often quite tenuous and significantly hampers our ability to derive confident conclusions.
At 47:05 Ehrman brings up Romans 1.3-4 for the first time during the debate. Ehrman lays out a basic case for finding an adoptionist Christology in this text. In a few months I will be publishing a series of posts addressing various interpretations of Romans 1.3-4, including a comprehensive analysis of various redaction theories. That series will be reasonably exhaustive. Thus, I will limit my comments here to those of direct pertinence to the debate.
Here is the NASB translation of the text:
3 concerning His Son, who was born of a descendant of David according to the flesh,
4 who was declared the Son of God with power according to the Spirit of holiness by the resurrection from the dead, Jesus Christ our Lord.
"With power" can also be translated "by power" or "in power". I prefer the latter.
Gathercole's first response, at 48:30, is to emphasize the level of speculation involved in determining whether a given text is a creed. He does, however, think that there's a good chance Romans 1.3-4 is a creed. Where he disagrees with Ehrman is that the creed presents something radically different than what Paul believed.
At 49:40 Gathercole says that it's much more speculative to say that Paul added "in power" to the creed. Ehrman's initial response seems to indicate that the inclusion of "in power" tells strongly against an adoptionist reading—Jesus became the "son-of-God-in-power" at his resurrection. Thus, if the creed originally taught an adoptionist Christology, "in power" would have to be absent. This is precisely what Ehrman argues: "in power" was probably a Pauline interpolation. Around the 51 minute mark, Ehrman lays out his principal argument for that conclusion—it's the only part of the second section that doesn't correspond to anything in the first section.
To see this, consider how Ehrman contrasts the elements of the creed in his book How Jesus Became God: 
A1 Who was descended
A2 from the seed of David
A3 according to the flesh,
B1 who was appointed
B2 the Son of God in power
B3 according to the Spirit of holiness by his resurrection from the dead
Since "son of God" corresponds to "seed of David", Ehrman argues, "in power" is left hanging.
Against Ehrman's argument we may adduce six responses. I will discuss these all more fully in my planned series on Romans 1.3-4:
1. We have to be careful what we conclude from parallelism arguments—it's highly speculative to assume everything will line up perfectly.
2. The strength of the argument is dependent on how we structure the creed. Scholars like Matthew Bates and Gordon Fee structure the various sections of the creed differently than Ehrman, making "in power" no longer unnecessary.
3. There are other parts of the creed that don't line up perfectly. For example, consider the phrases "according to the flesh" and "according to the Spirit of holiness". Technically, one could omit "of holiness" and still have an understandable creed. Someone might respond that the emphasis is on corresponding phrases, not word-for-word similarities—in that case, if "in power" modifies "Son of God" (as many scholars argue) it is no longer out of place. The same parallel dooms the response that "of holiness" is a necessary qualification for the office of "the Spirit"—"in power" could also be a necessary qualification for "Son of God".
4. Even if we accept Ehrman's structuring of the creed, James Dunn argues that "seed of David" and "Son of God" might have been regarded as insufficiently contrastive, because the seed of David was already considered to be the Son of God. Thus, "in power" preserves the antithetical parallelism.
5. There is precedent for this formulation in other Christological hymns (1 Tim 3.16, Heb 1.3).
6. "Son of God in power" is an expression not used by Paul elsewhere. This is not a particularly strong argument, but it's presence is slightly more probable if the expression originated elsewhere than if Paul used it himself.
Gathercole responds that scholars differ as to whether "in power" was there originally. He cites James Dunn's commentary arguing that "seed of David" and "son of God" don't contrast enough, and thus the "in power" is necessary to preserve the antithetical parallelism (point #4 above). At 54:13 Ehrman briefly responds: "My case doesn't rest on whether two words in Romans 1.3-4... there are other preliterary traditions that all point in the same direction." (ellipses indicate Ehrman's incomplete sentence, not an omission). While possibly due to time constraints, it's notable that Ehrman drops the issue after Gathercole provides Dunn's response. He then refers to his book, indicating that he makes a case there for viewing an adoptionist Christology as one of the earliest views.
Ehrman's comment that "there are other preliterary traditions that all point in the same direction" references passages in the speeches in Acts, though he doesn't bring them up in the debate. For engagement with these passages, see C. Kavin Rowe's paper "Acts 2:36 and the Continuity of Lukan Christology" and Michael Bird's book Answering Adoptionist Christology.
In conclusion, I think Gathercole had the upper hand in this discussion, though both scholars provided robust defenses of their views. The debate covered a lot of ground, though it would have been interesting to see Ehrman defend his redactional thesis for Romans 1.3-4 a bit more. Ultimately, this debate did what all good debates should: offer an introduction to two competing viewpoints and provide resources for further research.
References and Notes
 R. W. Hoover, "The Harpagmos Enigma: A Philological Solution," HTR 64 (1971), 95-119
 J. C. O'Neill, "Hoover on Harpagmos Reviewed, with a Modest Proposal concerning Philippians 2:6," HTR 81 (1988), 445-49
 Gordon Fee, Pauline Christology: An Exegetical-Theological Study. Hendrickson Publishers, 2007, 382
 Michael Wade Martin, "ἁρπαγμός Revisited: A Philological Reexamination of the New Testament's 'Most Difficult Word'," JBL 135 (2016), 175-94
 Bart Ehrman, How Jesus Became God: The Exaltation of a Jewish Preacher from Galilee. HarperOne, 2014. 166 (eBook)