A.T. Robertson Commentary Matthew 23:3

"all things therefore whatsoever they bid you, [these] do and observe: but do not ye after their works; for they say, and do not." — Matthew 23:3 (ASV)

For they say and do not (λεγουσιν κα ου ποιουσιν). "As teachers they have their place, but beware of following their example" (Bruce). So Jesus said: "Do not ye after their works " (μη ποιειτε). Do not practice their practices. They are only preachers. Jesus does not here disapprove any of their teachings as he does elsewhere. The point made here is that they are only teachers (or preachers) and do not practice what they teach as God sees it.