Conversation so far:
Who played Yoda?
CANNOTANSWER.
Why was Yoda important in this film?
In Revenge of the Sith, Yoda leads the Jedi Council in pursuing the mysterious Sith Lord Darth Sidious.
was he successful in this?
Yoda battles Palpatine in a lightsaber duel that wrecks the Senate Rotunda.
In the end, neither is able to overcome the other and Yoda is forced to retreat.
What else did Yoda do in the movie?
Additionally, they order him to spy on Palpatine, whom Anakin considers a friend and mentor.

Question: why did they spy on Palpatine?
Self-contained rewrite: Why did the Jedi Council spy on Palpatine Star Wars Episode III: Revenge of the Sith?