It may not be so significant, but it's the bit that I'm interested in!
I don't give a flyin' flip if it's possible or not, and "authentic theology" seems a bit of a loaded phrase to me, but I'm genuinely curious, now that the OP brought it up, as to the timing of the historical movement towards "a personal relationship with Christ."
It strikes me that the notion of a personal relationship rather than one sanctioned by a specially trained intermediary is a pretty significant turning point in the history of Christianity--actually, not just strikes me, along with selling indulgences, I was kinda under the impression this was one of the bits Martin Luther nailed to a door somewhere--and one that's maybe led to people carrying around their own weird personal theologies without ever having to check 'em against somebody else's. Early Catholicism, at least, seems to be to be rather opposed to the notion of the lay person having a personal relationship with Christ--that way lay heresy! (Even in modern Catholicism, I recall my grandmother calling on saints and Mary on a regular basis, but God not so often. One always got the impression that God was rather busy and should not be bothered except in dire emergence, whereas saints remembered what it was like to fight with your kids and could be safely invoked as a kindred spirit.)
It also seems to me that if one has a personal relationship with one's god, unfiltered by the braking effect of other people, one's a bit more likely to go completely off the rails. Not that priests are any more immune to crazy than anybody else, heaven knows, but if you have to stop and talk to another person about what you believe, you're probably more likely to think it over than if you're just stewing with the god inside your head.
So knowing when this bit became popularized would be interesting to know!