Star Wars: The Rise of Skywalker explains why Palpatine wanted Luke to kill him in Return of the Jedi. Emperor Palpatine is the great villain of the Star Wars saga, an evil so great his death was necessary to restore balance in the Force itself. The Skywalker saga is the story of Palpatine's rise to power, his defeat, and his attempt to regain power once again.
And yet, for all that's the case, the Emperor remains something of a cipher. He's less of a character than he is a force of nature; his evil doesn't have an origin, it simply is. And unfortunately that makes certain scenes rather difficult to interpret, because Palpatine lacks definition as a character. Take Return of the Jedi, where he initially attempted to persuade Luke Skywalker to strike him down. "The hate is swelling within you now," the Emperor taunted. "Take your Jedi weapon. Use it. I am unarmed. Strike me down with it. Give in to your anger." The common interpretation is that Palpatine was simply trying to provoke a duel between Darth Vader and Luke Skywalker, in order to figure out which one was more powerful. And yet, Palpatine really does seem quite eager to die.
Star Wars: The Rise of Skywalker reveals the reason. Palpatine had learned the secret of immortal life, a dark Force power called Essence Transfer. This allows a Sith to preserve their spirit upon death, by binding it to an object, a specific geographical place, or even another person. By the time of Return of the Jedi, Palpatine's body would be coming to the end of his natural life, and he would undoubtedly have been considering where to place his essence; that may well be why he had clones being created on the distant planet of Exegol in the first place. But the son of Anakin Skywalker, who had inherited all his father's power in the Force, would be an ideal host.
There's just one complication; according to Star Wars: The Rise of Skywalker, a dying Sith Lord's spirit can only possess someone if they are under the influence of the dark side at that time. "With your hatred you will take my life," Palpatine commanded his granddaughter Rey in Rise of Skywalker, "and you will ascend." That was why the Emperor taunted Luke all those years earlier, intending the Jedi to kill him in anger and thus fall under his influence. What's more, Palpatine probably expected Darth Vader to just stand by and watch; treachery has always been the way of the Sith, and he didn't expect the disloyal Vader to interfere. But Palpatine miscalculated, and Vader intervened, whether because he sensed what was about to happen or because of his conflicted loyalties. And so the Emperor pivoted to a backup plan, intrigued to see which one of the two Skywalkers triumphed.
Fans and critics alike generally view Star Wars: The Rise of Skywalker as a weak addition to the Skywalker saga, and an unsatisfying conclusion to the sequel trilogy. But, as poorly as the narrative is handled, many of the ideas are actually pretty interesting. In this case, Palpatine's knowledge of Essence Transfer adds new depth to Return of the Jedi, making that final battle on the Second Death Star all the more powerful.