“Jesus told his apostles to buy swords, but then he said three is enough, why?”
I think because it was just a symbolic gesture. He was to be “counted among the transgressors”, was the prophecy, and if you look at the Hebrew word used in Isaiah for “transgressor” it carries the sense of “rebel”. In fact, that was one of the accusations laid against Jesus, that he was instigating a revolt against the Roman authorities. Well, you can’t very well be a rebel if you don’t have any weapons.
He was to be “counted among the transgressors”,
Also the weapons could be symbolic but secularly speaking the number of weapons could have a lot to do with how his arrest turned out.