'Come-to-Jesus' is a common idiomatic adjectival phrase used across America and moving into other English-speaking countries. It is probably most often used in the phrase 'come-to-Jesus meeting', although you might also have a C-t-J speech or talk.
However you phrase it, it means a serious, shape up or ship out type speech. Your boss might invite you into her office for a come-to-Jesus speech to let you know that you are in danger of losing your job if you screw up again. In general 'coming to Jesus' (in the metaphorical sense) requires a bit of browbeating from your betters. Even so, it retains a vague positive connotation, as you are being browbeaten into doing The Right Thing.
This phrase most likely comes from the loud, charismatic pushiness of evangelical preachers, travelling the land and spreading The Word through forcible rhetoric and threats of eternal consequences. It is interesting to note that the earliest references to the phrase being used in this manner come from the late 1990s; this is a trendy buzzword, not a classic Americanism.