Charles Ellicott Commentary Matthew 21:27

"And they answered Jesus, and said, We know not. He also said unto them, Neither tell I you by what authority I do these things." — Matthew 21:27 (ASV)

We cannot tell — The confession of powerlessness to which the priests and scribes were led was, as has been said, a virtual abdication. Before such a tribunal, the Prophet whom they questioned could rightly refuse to plead. There was, indeed, no need to answer. For those who were not willfully blind and deaf, the words He had spoken, the works He had done, and the sinless life He had led were proofs of an authority from God.