When Sidious Knights Anakin as Darth Vader why does he talk like God?

And there we have it. The ultimate rush that comes in a huge burst and then trickles back down to it's original levels. Thus the constant change in voice.

 

When Anakin agrees with Palpatine's claim the Jedi will move against the Senate, my impression was that he probably didn't really believe it. At that point, he's made his bed, so he's just playing along. Palpatine is sort of helping Anakin to rationalize what he's about to do, but I think the two of them are both aware it is really just lip service. It is power they both want.

But when Anakin pledges himself to Sidious, yeah, he's under the spell of the Dark Side. It adds an epic mystique, I think. Sort of a (very well-developed) transition in tone to the world of the OT. I got chills the moment the Emperor spoke: "Your fulfilling your destiny, Anakin." The old Star Wars was back

 

Anakin was brainwashed.
When you see Skywalker bow before the Dark Lord, we hear Sidious's voice drop into a deep, demonic drawl - he is inside Anakin's head. Anakin will be haunted by this voice for the rest of his life - it is the same disembodied voice speaking to Anakin when he is waiting in the Jedi Council. "If I die, my knowledge dies with me." (paraphrase?)

This is what it is like to be mind tricked by the Sith. This is how "hundreds of senators are under the influence of a Dark Lord of the Sith." These senators aren't weak minded people - the Sith can literally, physically "twist your mind", as Obi-Wan says.

Palptine drills his lies into Anakin's skull.

PALPATINE
"The Jedi's next move will be against the Senate."
ANAKIN
"I agree, the Jedi will soon attack the Senate."

Anakin repeats and agrees with everything Sidious says, like he's hypnotized. He has no reason to believe the Jedi would attack the Senate. He has lost his soul and his mind to Sidious - it sounds like The Emperor actually inhales Anakin's soul when Young Skywalker bows before him.

"Don't underestimate the powers of the Emperor"

Look at Dooku. Qui-Gon Jinn, his own apprentince, was murdered by the Sith - Dooku knew this but turned to the darkside anyway. Anyone - even those who join the Sith with the intention of destroying them - who lowers their guard to the Sith make themselves vulnerable to their mind warping powers.

This makes the Luke situation at the climax of ROTJ all the more perilous. Sidious is trying to con Luke into feigning alliegance to the Sith to save his friends. Merely feigning alliegance to the Sith gives Sidious enough of a hole to get inside your head and rearrange your thoughts and beliefs. Sidious knew he wouldn't be able to argue Luke over to the darkside - all he needed was an opening. Its kind of like inviting a vampire into your house. Even if you do so with the intention of killing the vampire - by opening your door to the evil spirit, you've allowed yourself to become helpless to its grip. And like a vampire, the Sith's poisonous venom can transform anyone into a monster.
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I agree with this one. All the Emperor needed was an "ok...maybe I'll join. " from Luke to start filling his brain with poison. That's why he tried so hard to get him to accept his "Destiny."

Just because Anakin fell under his power here, however, does not mean that he was forever stuck in this trance. No, I think this only happens to the Sith Apprentice once. Because once Palpatine has twisted you with his power, he doesn't need to any longer. That one period of mind-tricking is enough.

Even if he were always locked in some hypno-trick, I think this actually helps the ROTJ situation all the more. For me, the Power of love is what defeated the Emperor. It was Anakin's love for his family that brought him back. If the desire to save his son was stronger than the Emperor's power, I say that is fantastic. It only helps to make the point. There is no harm in it.

 

Ben: "Your father was seduced by the Dark Side of the Force."

To turn a Jedi into a Sith, they must be seduced by the allure of power. They must be willing to ignore the Jedi teachings in favor of the Sith Arts. Note that as soon as it's done, Palpatine returns to normal.