After laying down the ground rules, the first thing that I think we need to tackle is why the early Christians began to construct the picture(s) of Jesus they did? In other words, what inspired them to form their first christologies? What impulse(s) caused them to want to understand Jesus in "divine" categories beyond their memories of him as their Jewish teacher and leader?
These are not easy questions for sure, and it is necessary to keep in mind that a complex of impulses worked in conjunction with each other to form Christology. As Christianity mobilized and became geographically more and more diverse, the Christological formulations will also diversify. My study of the literature has revealed three major Christological paradigms that are connected with different geographical locales. So I will discuss diversity very shortly.
For now, let's just consider impulse. Why develop Christological schema at all?
One of the strongest impulses I have been able to recover from the literature is the need for the early Christians to attach some meaning or value to the troubling death of Jesus. Allusions and interpretations of his death are across the literature, deeply engrained from the very beginning of Christianity. Yes, even in Q, and even in Thomas. Both know Jesus died, and both offer meaning to that death. Now our different sources know or offer different meanings for his death, but know about it they do.
Why was it so troubling? Because he died as a Roman criminal. His criminal death was a problem that I cannot overemphasize. It was good for nothing in terms of theology. It was not good for trying to convert Romans, and it was not good for trying to convert Jews. It in fact was a liability that the Christians apologize for and explain over and over and over again in their literature.
But we can imagine from the explanations they provide for Jesus' death that some of their first questions following Jesus' death were likely along these lines:
Why was our leader killed as a criminal?
Why did God allow this to happen?
Where was Jesus now?
What would happen next?
What are we supposed to do now?
A second impulse that I think we have to take very seriously, again because it is all over the various layers of traditions (age and geography), were the followers' claims to visions of Jesus after his death. They claimed to have apocalypses of Jesus, to see him or talk to him after he died. Although we might see these as only their stories, it is clear from their writings that they understood these visions to be significant religiously. And because of this, their religiously interpreted experiences influenced sharply the development of Christology.