Albert Barnes on Matthew 21:24-25

And Jesus answered etc. Jesus was under no obligation to give them an answer. They well knew by what authority he did this. He had not concealed his power in working miracles, and had not kept back the knowledge that he was the Messiah. He therefore referred them to a similar case--that of John the Baptist He knew the estimation in which John was held by the people. He took the wise in their own craftiness. Whatever answer they gave, he knew they would convict themselves. And so they saw, when they looked at the question. They reasoned correctly. If they said, From heaven, he would directly ask why they did not believe him. They professed to hear all the prophets. If they said. Of men, their reputation was gone, for all the people believed that John was a prophet.

The baptism of John. For an account of this, see Matthew chapter 3. The word baptism here probably includes all his work. This was his principal employment; and hence he was called the Baptist, or the Baptizer. But our Saviour's question refers to his whole ministry.-- "The ministry of John, his baptism, preaching, prophecies--was it from God, or not?" If it was, then the inference was clear that Jesus was the Messiah; and then they might easily know by what authority he did those things.

From heaven. By Divine authority, or by the command of God.

Of men. By human authority.