Bultmann's notorious claim that “I do indeed think we can know almost nothing concerning the life and personality of Jesus” is on one level overstated and easy to dismiss. There are lots of things that we can know about the life of Jesus with a degree of confidence, his healing activity, his proclamation of the kingdom, his connection to John the Baptist, the call of disciples who continued the movement after his arrest and crucifixion, and so on. Beginning from this kind of secure information, one can produce a good sketch of the life of Jesus, and E. P. Sanders has illustrated how much one can do with this kind of data when we integrate them into an informed understanding of Jesus' historical context.
But knowing things about the historical Jesus is not the same as being able to write his biography. Bultmann rightly pointed out that we do not have the data available to trace his psychological development in the manner of contemporary biography. Yet recent years have seen an increasing confidence in our ability to paint something approaching a complete picture of Jesus' life and personality, as if all the relevant and necessary materials for that complete picture are available somewhere. It just takes a bit of effort to get at them. We spend many painful hours sifting and honing criteria because we feel that the literary deposit is somewhere bound to contain all the material of real importance. Only matters peripheral to the task of reconstructing the key elements in his life have disappeared.
This kind of assumption develops out of an unrealistic perspective on the task. We proceed as if we are doing the work of restoration, clearing the dirt, the damage, the rust in order to unveil the real Jesus. But the quest is not about restoration. It is a task of ancient history and when understood as ancient history, discussion about the historical Jesus should constantly involve the reminder that massive amounts of key data must be missing.
The problem is that we are in denial. We simply do not want to admit that we do not have all the data we need to paint a complete picture of the historical Jesus. Good scholarship is sometimes born from a desire to fill in the gaps, and informed speculation can be a virtue. But over-confidence born out of an unrealistic expectation of the evidence will make future generations wonder what we were playing at.
I think we agree.