The early Christian movement was interested in the genuinely past history of Jesus because they regarded it as religiously relevant. But why should this have been the case? Dunn offers a sociological explanation: The early Christians, distinguished from other groups by terms referring to Jesus ("Nazarenes" and "Christians"), "would almost certainly have required a foundation story (or stories) to explain, to themselves as well as to others, why they had formed distinct social groups" (Jesus Remembered, 175). It was for purposes of self-identity that Christians transmitted Jesus traditions and wrote Gospels. While this explanation has the advantage of cross-cultural comparison, it is lacking in the cultural specificty necessary for an adequate explanation. Early Christians were less concerned with self-identity than with salvation, though the two are in their case closely related. Jesus was more than the founder of their movement; he was the source of salvation. Moreover, this salvation was understood within the thoroughly Jewish context of Christian origins. It was fulfillment of the promises made by the God of Israel to his people Israel in the past. It was a new chapter--the decisive, eschatological chapter--in God's history with his people and the world. The events of Jesus' history were charged with all the history-making significance of the activity of Israel's God. Thus, at the deepest level, it was for profoundly theological reasons--their understanding of God and salvation--that early Christians were concerned with faithful memory of the really past story of Jesus. The present in which they lived in relationship with the risen and exalted Christ was the effect of this past history, presupposing its pastness and not at all dissolving it.
--pp. 277-78 (italics original)
Schlatter and Cullmann are applauding in their graves!