5 “Pilate said unto Him, What is truth?” Nor did he wait to hear the answer; but “when he had said this, he went out again unto the Jews, and said unto them, I find in him no fault. But you have a custom that I should release unto you one at the passover: will you therefore that I release unto you the King of the Jews?” I believe when Pilate said, “What is truth?” there immediately occurred to his mind the custom of the Jews, according to which he was wont to release unto them one at the passover; and therefore he did not wait to hear Jesus' answer to his question, What is truth?
To avoid delay on recollecting the custom whereby He might be released unto them during the passover— a thing which it is clear he greatly desired. It could not, however, be torn from his heart that Jesus was the King of the Jews, but was fixed there, as in the superscription, by the truth itself, whereof he had just inquired what it was. “But on hearing this, they all cried again, saying, Not this man, but Barabbas. Now Barabbas was a robber.” We blame you not, O Jews, for liberating the guilty during the passover, but for slaying the innocent; and yet unless that were done, the true passover would not take place.
But a shadow of the truth was retained by the erring Jews, and by a marvellous dispensation of divine wisdom the truth of that same shadow was fulfilled by deluded men; because in order that the true passover might be kept, Christ was led as a sheep to the sacrificial slaughter. Hence there follows the account of the injurious treatment received by Christ at the hands of Pilate and his cohort; but this must be taken up in another discourse.
Source: Tractates on the Gospel of John (New Advent)