John Gill

But ye have a custom,.... Not a law, either of God or man's, but a custom; and which was not originally observed at the feast of the passover, and perhaps was not of any long standing; but what the Roman governors, by the order of Caesar, or of their own pleasure, had introduced to ingratiate themselves into the affections of the people; and being repeated once and again, was now looked for: that I should release unto you one at the passover; which was at this time; and more than one it seems it was not customary, to release: will ye therefore that I release unto you the King of the Jews? who they had said called himself so, and was so accounted by others, and which Pilate says, in a sneering, sarcastic way; though he was heartily willing to release him, and was in hopes they would have agreed to it, since nothing could be proved against him; however, he proposes it to them, and leaves it to their option.