The problem is that - as usually presented - Christianity is historical. Jesus was someone who lived a long time ago, and we are supposed to learn 'about' him from historical sources (mostly the New testament).
The most important thing is apparently that Jesus a left a set of instructions about how to live, and prohibitions about what not to do - but in a scattered and somewhat confusing form. And again, can we really be sure that all this information is correctly recorded, and the we have understood it correctly?
Can we be sure enough to gamble everything upon the accuracy of what we know?
All this stuff is very remote in time and space, and apparently very tenuous (as is natural for any kind of history, any kind of law, philosophy or other discipline) - really, it is all much too uncertain to pin all of one's hopes on; too uncertain to be the basis for a transformation of life...
Thus one side of the Christian tradition - and one that seems pretty dominant. But there is another side to the story.
Jesus is alive, he is active in the world. And Jesus is personal - we can have an actual, here and now relationship - whoever we are, wherever we are. And this Jesus is concerned with each of us as a specific and unique individual.
According to this other side, in principle, Jesus need not be historical; we need not rely upon the accuracy of the test and our understanding of the text; because there is an active, current, relationship between him and you, me, anybody.
Presumably, by this relationship, Jesus can 'tell' us (in some way which cannot be misunderstood) anything and everything that we need to know.
But for this to happen requires that we have a perspective on life (more exactly, a set of metaphysical assumptions) in which this putative relationship with Jesus is coherent, possible, sufficiently-plausible such that we could seek, recognise, and respond to the personal relationship that he (supposedly) offers.
It is the lack of this perspective, and resistance to it; that so effectively blocks so many people from Christianity.
