This one is for Mhairi Simpson, to whom I had to explain this phrase over the weekend.
In the South, there is a particular phenomena referred to as a Come to Jesus Talk. As in:
If you don’t clean your room, we’re gonna be having a come to Jesus talk, young man.
To my mind, the origins of this particular phrase have to do with the…shall we say missionary nature of much of religion in the Bible Belt. For certain segments of the population, it is considered a religious duty to spread the faith. Which sometimes means that complete strangers may accost you in Walmart to ask if you’ve accepted Jesus Christ as your one and only savior. (True story, this happened to me twice. Same old dude. Which is a double whammy because you aren’t ever rude to old people in the South. I’ve learned to watch for him and make a quick turn down another aisle to avoid him now because evidently he doesn’t trust the state of my salvation to the Episcopal Church.) The notion being that if you haven’t, it’s their duty to have a Serious Discussion with you about the importance of coming to Jesus–because the state of your eternal salvation is OBVIOUSLY a total stranger’s business…and your own personal religious beliefs (should they be different) are totally irrelevant to the discussion. (That’s a whole other kettle of fish).
In much older times, I suspect there was a level of threat that went along with this–which I always kind of imagine as being press-ganged into religion, and it’s this latter interpretation that gives rise to the adjectival use of the term. Used as an adjective, Come to Jesus has connotations that you better be right with the Lord because if you don’t do whatever it is that’s in question, the fate of your eternal salvation is gonna be of immediate relevance. Think of it as a combination intervention/threat that you better shape up about whatever it is that’s the subject of the Come to Jesus Talk. So it’s a form of getting called on the carpet or held accountable for something. With, usually, a healthy dose of dressing down and guilt tripping.
*There may be other interpretations of this phrase. This is mine after a lifetime of observations made while growing up in the buckle of the Bible Belt.