Adam Clarke on Matthew 27:21

They said, Barabbas - What a fickle crowd! A little before they all hailed him as the Son of David, and acknowledged him as a gift from God; now they prefer a murderer to him! But this it appears they did at the instigation of the chief priests. We see here how dangerous wicked priests are in the Church of Christ; when pastors are corrupt, they are capable of inducing their flock to prefer Barabbas to Jesus, the world to God, and the pleasures of sense to the salvation of their souls. The invidious epithet which a certain statesman gave to the people at large was, in its utmost latitude, applicable to these Jews, - they were a Swinish Multitude.