“Jesus found a young donkey and rode on it, fulfilling the prophecy…” (John 12:14 NLT)
Even more important for the Palm Sunday story is the prophetic Zechariah’s promise, given to the Jews five hundred years before the time of Christ: “Rejoice, greatly, O daughter Zion! Shout aloud, O daughter Jerusalem! Lo, your king comes to you; triumphant and victorious is he, humble and riding on a donkey.” (Zechariah 9:9 NRSV) Everyone in the crowd would have known these words and their promise of who would come riding on a donkey, so that when Jesus met up with His disciples and mounted the donkey, the people knew instantly what was happening. He was giving a clear signal that He was the long-awaited King promised by the prophets. Finally, Jesus was openly proclaiming He was the Messiah!
-- Adam Hamilton in “The Way: Following in the Footsteps of Jesus”