20:1-8 Men often pretend to examine the evidences of revelation, and the truth of the gospel, when only seeking excuses for their own unbelief and disobedience. Christ answered these priests and scribes with a plain question about the baptism of John, which the common people could answer. They all knew it was from heaven, nothing in it had an earthly tendency. Those that bury the knowledge they have, are justly denied further knowledge. It was just with Christ to refuse to give account of his authority, to those who knew the baptism of John to be from heaven, yet would not believe in him, nor own their knowledge.See this passage explained in the notes at Matthew 21:23-27. 7. could not tell—crooked, cringing hypocrites! No wonder Jesus gave you no answer (Mt 7:6). But what dignity and composure does our Lord display as He turns their question upon themselves! See Poole on "Luke 20:3"

And Jesus said unto them,.... Since they would not give him a direct answer to his question:

neither tell I you by what authority I do these things; nor was there any need of it; they might easily perceive by what he had said, from whence he professed to have received his authority, from God, and not men; See Gill on Matthew 21:27.

And Jesus said unto them, Neither tell I you by what authority I do these things.