Here are my summary reasons as to why the Historical Jesus Quest is such a massive task:In the final analysis, I suppose one can't get away from the fact that our historical analysis carries us to point X but it is "faith" that carries us to the next step of saying, the data is reliable enough that I'll follow Jesus for the morality we believe he expoused and the theological significance of his life, death and resurrection.
(1) So much data is missing, e.g. there is so little on Jesus’ life before 30.
(2) The data we do have is highly prejudiced, mainly pro-Christian propaganda.
(3) The sources we have are disputed -- different scholars value the sources differently
(4) The sources are sometimes contradictory and difficult to interpret.
(5) Our distance from the data is so great - we read our own prejudices into the texts.
(6) And now there is so much secondary literature available that it is difficult to navigate our way through it all.
(7) Jesus is a figure in whom so many have a stake, and the quest is often controversial.
I will go on to tell the students, though, that the news is not all bad. We are actually surprisingly well informed about Jesus compared to many other figures from the ancient world.
[ed. note - emphasis mine]
The "modern" mind has the unwritten assumption that reason is the only source of truth or the most reliable source of truth.
Historical analysis is not without reason as it is of the same feather as legal-forensic analysis (i.e. CSI stuff!) in that you piece together physical evidence with eyewitness testimony so that you can arrive at an approximation of what you think happened at the crime scene.
In the case of Christianity, these approaches can help us figure out what happened 2000+ years ago. There is no doubt that the distance in time and culture makes it more challenging.
Alas, in typical "lunch table" conversation with skeptics of Jesus, they claim what we know about Jesus was all fabricated at worst or confused at best. Once they start with that assumption, the conversation tends not to go very far.
Aside from providing an honest presentation of Jesus by acknowledging what we know and what the limits are to what we know, I need to be praying that my life would be transformed.
For me, one of the most striking "evidences" for the Jesus of the Bible is that the lives of the disciples were changed and that the early Christian community and for that matter Christians through the ages were thoroughly changed by their belief in Jesus. Thus, today, in my exhibiting a transformed life, skeptics would hopefully give Jesus a second look and continue the search.