“Say to the daughter of Zion, ‘Behold, your king is coming to you, humble, and mounted on a donkey, on a colt, the foal of a beast of burden.’ ”” (Matthew 21:5, ESV)

Frederick Meyer in his book Through the Bible Day by Day Devotional Commentary, comments here:

Remember that ancient prediction quoted here, Isa. 62:11, and especially Zech. 9:9. The King comes having salvation. That is the divine order! We shall never know the full power of Christ’s salvation until we have welcomed him to our hearts as King. Matthew 20:29

Well! I couldn’t put it any better than that.