The neat thing about this doctrine is that it completely screws up a bunch of other doctrines.
POPS: So, you ready to Incarnate and get brutally tortured to death?
JC: Um, sure, if You say so. Sounds kind of unpleasant though. Why do I gotta do that?
POPS: So I can free mankind which I created from Original Sin which I also created.
JC: Er, I guess that makes sense, but couldn't You just --
POPS: Hey! I forgot to mention, the girl I'm going to grow you out of? You'll love this: I totally preserved her from the stain of Original Sin!
JC: Wow, how'd you do that?
POPS: Oh, you know, Sanctifying Grace and all.
JC: So, couldn't You --
POPS: Okay, time to go! Merry Christmas!
JC: Wha?