4 “When Pilate, therefore, heard that saying, he was the more afraid; and entered again into the judgment hall, and says unto Jesus, Whence are you? But Jesus gave him no answer.” It is found, in comparing the narratives of all the evangelists, that this silence on the part of our Lord Jesus Christ took place more than once, both before the chief priests and before Herod, to whom, as Luke intimates, Pilate had sent Him for a hearing, and before Pilate himself; so that it was not in vain that the prophecy regarding Him had preceded, “As the lamb before its shearer was dumb, so He opened not His mouth,” especially on those occasions when He answered not His questioners.
For although He frequently replied to questions addressed to Him, yet because of those in regard to which He declined making any reply, the metaphor of the lamb is supplied, in order that in His silence He might be accounted not as guilty, but innocent. When, therefore, He was passing through the process of judgment, wherever He opened not His mouth it was in the character of a lamb that He did so; that is, not as one with an evil conscience who was convicted of his sins, but as one who in His meekness was sacrificed for the sins of others.
Source: Tractates on the Gospel of John (New Advent)