Sidious+Vader+Luke=3

The good is still in Vader and he saves his son Luke. Vader is just a brave and interesting and complicated character.

 

The quote is more like this:

"It was a shame, almost, that he couldn't let Luke kill the Emperor yet. If he did that, there was a chance he might go back to his friends. So, Vader had to shepherd him through periods like this, to keep him from doing damage in the wrong places-or the right places prematurely."

 

George Lucas wrote the story and according to his interview with Jim Moyers, Sidious and Vader were trying to knock each other off with Luke. So yes it is safe to say Lucas knows what his characters are thinking since he created them.

 

This could signal the start of Vader's "turning" towards Luke, and thus not wanting his son to fall to the Dark side
That's an interesting idea (never considered that). However, it doesn't explain why Vader pressed the attack...and provoked Luke into attacking him with the "perhaps, she will" line?

I think Vader's block of Luke was some of the last bits of his Dark Side instinctivly kicking in to protect his "master." Palpatine knew Vader would not allow Luke to strike him down, and it sparked the confrontation he wanted (father/son) either he would have a new apprentice...or his trusted Sith Lord would prove his continued worth.

I think GL has kept the "rule of 2" intact, because only 2 of the men in that room would survive. And Palpatine's "overconfidence" made him believe that whatever happened he would come out on top. Only both Skywalkers proved him wrong.

 

Vader kept Luke from striking down the Emperor to keep his journey towards the Dark Side from being complete. Luke was inches away from being on the Dark Side but his loving father stopped him from doing something he would regret later.