Near the end of the movie, Rey encounters emperor Palpatine who demands that she strike him down in anger so that he and the Sith can continue to rule through her. This is almost identical to the "offer" he makes to Luke in ROTJ, though he seems to be even more forthcoming with Rey since he even admits that he hopes to essentially possess her afterwards.
My question is, why tell the hero this? If he really wants them to go through with it, why show them that it's all part of his evil plan? Wouldn't that make them less likely to want to strike him down? Why not try to goad them into it without making it apparent that it is exactly what he wants?
Having thought about it a while I've come up with a few personal theories, none of which I find very convincing.
- The hero (Rey or Luke) needs to be made fully aware of the consequences of their action for the plan to work. Only if Rey knew and accepted that she would become corrupted after killing Palpatine would she truly fall to the dark side. If this is true, striking Palpatine down in anger is not so much what causes the hero to fall as the submission to his will.
- Palpatine is using reverse psychology to prevent the hero from actually killing him, waiting for them to let their guard down so he can turn the tables and kill them instead.
I favor #1 a lot more than #2, but I wonder if there's a better explanation.