Adam Clarke on Matthew 21:27

We cannot tell - Simplicity gives a wonderful confidence and peace of mind; but double dealing causes a thousand inquietudes and troubles. Let a man do his utmost to conceal in his own heart the evidence he has of truth and innocence, to countenance his not yielding to it; God, who sees the heart, will, in the light of the last day, produce it as a witness against him, and make it his judge.

We cannot tell, said they; which, in the words of truth, should have been, We will not tell, for we will not have this man for the Messiah: because, if we acknowledge John as his forerunner, we must, of necessity, receive Jesus as the Christ.

They who are engaged against the truth are abandoned to the spirit of falsity, and scruple not at a lie. Pharisaical pride, according to its different interests, either pretends to know every thing, or affects to know nothing. Among such, we may meet with numerous instances of arrogance and affected humility. God often hides from the wise and prudent what he reveals unto babes; for, when they use their wisdom only to invent the most plausible excuses for rejecting the truth when it comes to them, it is but just that they should be punished with that ignorance to which, in their own defense, they are obliged to have recourse.