John Gill Commentary Matthew 21:24

"And Jesus answered and said unto them, I also will ask you one question, which if ye tell me, I likewise will tell you by what authority I do these things." — Matthew 21:24 (ASV)

And Jesus answered and said to them
Not by replying directly to their question, but by putting another question to them, whereby he escaped the snare he saw they laid for him:

I also will ask you one thing ,
word, or question,

which if you tell me ;
honestly, and plainly answer to it,

I likewise will tell you by what authority I do these things :
which was putting the thing upon such a foot, and in such a form, as they could not well object to; for Christ promises, that if they would return a plain answer to the question he had to put to them, and which was no unreasonable, nor impertinent one, he would thoroughly satisfy them in this point; and expressly declare his commission and authority, what it was, and from which he had it. The question is as follows: