Obi-Wan is a Jedi Knight.

He gives Luke a weapon on the first day of his journey as his 'squire'.

He insists that Luke must kill Vader.

Yoda is a Jedi Master.

His message is wars don't make one great and Luke shouldn't be too reliant on his weapons and should face his fear (that he will become as Vader) and conquer that fear (at no point does he tell Luke he has to kill Vader).

Luke faces Vader and refuses to kill him.

Ultimately it's Yoda Luke listens to, that is how he wins.

It's this example he passes on to his father which redeems him.

Yoda and Palpatine are above hacking at each other with blades.

Remember Yoda can pick up spaceships with his mind and Palpatine can make lightning come out of his fingers.

It defuses their power to be doing something so pedestrian.