Originally posted by Azronger
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Luke being his greatest adversary can be attributed to the fact that he made Vader chuck him down a hole and led a rebellion that toppled his empire.
Because the quote wouldn't make sense if it was. The tense of the quote is in the present, highlighting Luke's current feelings. And then it abruptly shifts to a past tense saying it "would" shake Luke's soul? No. It's discussing how even "the most powerful Jedi" would be shaken by Palpatine, emphasizing Luke's current dilemma since he's anything but.