For here is clear and plain prophecy: When Christ shall ride into Jerusalem, He will not come, as worldly kings are wont, on a proud steed, clothed in armor, with implements of war, but He will come, as the Evangelist says, meek, or as the prophet terms it, lowly. It is as if the prophet would thus warn everyone, saying: Mark well the ass, and know that He who comes on it is the true Messiah. Therefore, beware; do not look for a golden crown, sumptuous apparel or costly ornaments, or any great display. For Christ will come poor, with a meek and lowly heart, and will not be seen otherwise than riding upon an ass. This is all the pomp and glory He will show the world at His entry into Jerusalem.
This prophecy {Zechariah 9:9) induced our Lord now to make this entry, and He attaches much importance to it. Therefore He also gives the disciples such strict command about this matter; and will not enter Jerusalem by night, or secretly, but openly in the full light of day; not alone, but in the midst of a great multitude of. people going before and following after, calling aloud to Him as the true Son of David, and wishing Him great prosperity in His kingdom. Jerusalem must know of this entry, must see and hear the ass and this poor King, concerning whom Zechariah had prophesied, warning the Jews not to be offended at His poverty and humble entry, but to dismiss their idea that Christ would come with great worldly pomp. He will indeed be a king, says Zechariah, but a humble, poor king, who has nothing of the appearance of a king, judging by the outward pomp which worldly kings and princes usually show before men. (Luther’s House Postil, Sermon for the 1st Sunday in Advent, Volume 1, p. 18-19)