Pseudo-Chrysostom — as excerpted in the Catena Aurea on Matthew 21:1-9

“Men are likened to animals, from some resemblance they bear in their not recognising the Son of God. And this animal is unclean, and beyond all other brutes incapable of reasoning, a stupid, helpless, ignoble drudge. Such were men before the coming of Christ, unclean with divers passions; unreasoning, that is lacking the reason of the Word, stupid, in their disregard of God; weak in soul, ignoble, because forgetting their heavenly birth they became slaves of their passions, and of the dæmons; drudges, because they toiled under the load of error laid upon them by the dæmons, or the Pharisees. The ass was tied, that is, bound in the chain of diabolic error, so that it had not liberty to go whither it would; for before we do any sin we have free will to follow, or not, the will of the Devil, but if once by sinning we have bound ourselves to do his works, we are no longer able to escape by our own strength, but, like a vessel that has lost its rudder is tossed at the mercy of the storm, so man, when by sin he has forfeited the aid of Divine grace, no longer acts as he wills, but as the Devil wills. And if God, by the mighty arm of His mercy, do not loose him, he will abide till death in the chain of his sins. Therefore He saith to His disciples, Loose them, that is, by your teaching and miracles, for all the Jews and Gentiles were loosed by the Apostles; and bring them to me, that is, convert them to My glory.”