Luke is one of my favorite Star Wars characters. And there's a lot to like about him. But the one thing about Luke that resonates with me so strongly is that fact that he saw good in Vader. Keep in mind that Vader is guilty of many crimes, including several counts of the sci-fi variation of crimes against humanity. This is the guy who killed all the Jedi in the Jedi Temple, including the kids. And in my mind, murdering children is far worse than genocide. Vader was not responsible for the destruction of Alderaan in the way Governor Tarkin was. But he was still complicit in it to the point of keeping Leia in line. This is the guy who harmed his own children. He interrogated Leia using torture in A New Hope and chopped Luke's hand off in The Empire Strikes Back. And if that wasn't enough, Vader tried to lure Luke to the dark side when he was weak in both body and spirit a few scenes later.
Given that Vader chopped his hand off and then traumatized him with the "I am your father" bombshell, Luke had every reason to demand retribution. But he didn't. On the contrary, he went out of his way to save Vader, event to the point of willingly turning himself in to the Imperials, despite Obi-Wan and Yoda both telling him that Vader was a lost cause and the way he would ascend to the rank of Jedi Knight was to confront Vader again and kill him. He knew that there was still good in Vader, asserting as much to Obi-Wan, Leia, and even his father. Obi-Wan and Yoda were concerned with Vader as a public safety threat, but Luke chose to extend mercy to his father.
While Vader's exterior actions indicated an unrepentant attitude, the internal conflict raging told an entirely different story and Luke sensed this. And in the end, Vader's love for Luke triumphed over his dependence and loyalty to the Emperor and the dark side. It was Vader's love for his son that led straight to his redemption.
I've said this in a previous entry and I'll say it again: The message of redemption lies at the very heart of Star Wars. And Luke and Vader's story captures it so perfectly.