Albert Barnes on Matthew 23:2

Scribes and Pharisees. Mt 3:7.

Moses' seat, Moses was a legislator of the Jews. By him the law was given; and the office of explaining that law devolved on the scribes and Pharisees. In the synagogues they sat while expounding the law, and rose when they read it. By sitting in the seat of Moses we are to understand authority to teach the law. Or, as he taught the nation by giving the law, so they taught it by explaining it.

(r) "The Scribes" Mal 2:7