And they reasoned with themselves saying
Privately; perhaps, they withdrew at a little distance for a short time, and consulted among themselves what answer to return; and the amount of their reasonings were this;
if we shall say from heaven, he will say, why then did ye not
that is, should they say that John had a divine commission for what he said and did, they were aware that Christ would reply, why did not ye give credit to him? and had you done so, seeing he testified of me, you would have had no occasion to have put the above question; (See Gill on Matthew 21:25).