Another Christian Theory
maybe Christian really does work for MIB because he can’t leave the island like Jacob. Christian was responsible/had a hand (met some of them) in a lot of the Losties getting to the island. I think only Hurley and Locke (out of what’s left of the main characters) didn’t. Abbadon(sp?) who worked for Widmore had the biggest influence in getting Locke to the island post paralysis. Just something to think about.
Jack saw Christian off island after he left.