“Rejoice greatly, Daughter Zion! Shout, Daughter Jerusalem! See, your king comes to you, righteous and victorious, lowly and riding on a donkey, on a colt, the foal of a donkey.”
See, this was the day that the Passover Lamb was traditionally chosen to take away the sins of the people. On this day, the people rejected the Lamb because they wanted a Lion instead.