This is, and will remain, one of the hardest things to anwser.
On one hand we have the movie and our eyes, we have GL commentary, and we have Stover and this (which took me sweet time to do):
Click here to see the hidden message (It might contain spoilers)
"If you only knew," he said softly, perhaps speaking to the Jedi
Masters, or perhaps to himself, or perhaps even to the scarlet blade lifted
now as though in mocking salute, "how long I have been waiting for this ..."
….Within the public office of the Supreme Chancellor of the Galactic Republic, a last Jedi Master battled alone, blade-to-blade, against a living shadow. Sinking into Vaapad, Mace Windu fought for his life.…. This was Vaapad's ultimate test…. The shadow he fought, that blur of speed-could that be Palpatine?….. Mace was deep in it now: submerged in Vaapad, swallowed by it, he no longer truly existed as an independent being. Vaapad is a channel for darkness, and that darkness flowed both ways. He accepted the furious speed of the Sith Lord, drew the shadow's rage and power into his inmost center-……He had learned that it is fear that gives the darkness power. He was not afraid. The darkness had no power over him. But- Neither did he have power over it……Impasse. Which might have gone on forever, if Vaapad were Mace's only gift…..Feeling for its shatterpoint……He could feel the end of this battle approaching, and so could the blur of Sith he faced; in the Force, the shadow had become a pulsar of fear. Easily, almost effortlessly, he turned the shadow's fear into a weapon…..Out where Mace could flick his blade in one precise arc and slash the shadow's lightsaber in half….."For all your power, you are no Jedi. All you are, my lord," Mace said evenly, staring past his blade, "is under arrest."…… "Save your twisted words, my lord. There are no politicians here. The
Sith will never regain control of the Republic. It's over. You've lost." Mace leveled his blade. "You lost for the same reason the Sith always lose: defeated by your own fear." Palpatine lifted his head. His eyes smoked with hate. "Fool," he said….."Fool!" His voice was a shout of thunder. "Do you think the fear you feel is mine?" Lighting blasted the clouds above,…..Mace didn't have time to comprehend what Palpatine was talking about; he had time only to slip back into Vaapad and angle his blade to catch the forking arcs of pure, dazzling hatred that clawed toward him….Because Vaapad is more than a fighting style. It is a state of mind: a channel for darkness. Power passed into him and out again without touching him….That was when Mace finally understood. He had it. The key to final victory. Palpatine's shatterpoint. The absolute shatter-point of the Sith. The shatterpoint of the dark side itself. Mace thought, blankly astonished, Palpatine trusts Anakin Skywalker….. "I need him alive!" Skywalker shouted. "I need him to save Padme!" Mace thought blankly, Why? And moved his lightsaber toward the fallen Chancellor…..
This remains a thing I can't trully anwser.