A.T. Robertson Commentary Matthew 23:2

"saying, The scribes and the Pharisees sit on Moses seat:" — Matthew 23:2 (ASV)

Sit on Moses' seat (επ της Μωυσεως καθεδρας εκαθισαν). The gnomic or timeless aorist tense, εκαθισαν, not the aorist "for" the perfect. The "seat of Moses" is a brief form for the chair of the professor whose function it is to interpret Moses. "The heirs of Moses' authority by an unbroken tradition can deliver ex cathedra pronouncements on his teaching" (McNeile).