“Because he’s afraid of your power. The force chose you, Rey, the same way it chose my grandfather. Now only you can decide the fate of the Galaxy.”
“What Palpatine doesn’t know is that we’re a dyad in the force. Two that are one. We’ll kill him, and take the fleet. Together.”
This explains that Palpatine wants her dead because he doesn’t want to mess with another chosen one since he got killed by one before.
This also makes Anakin’s line at the end about bringing back balance much cooler.