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

“Never before had the Lord employed the services of beasts, nor surrounded Himself with the ornaments of green boughs, till now when He is going up to Jerusalem to suffer. He moved them that beheld to do that which they had before desired to do; so it was opportunity that was now given them, not their purpose that was changed.”