I will be serving for the Sacred Triduum at my FSSP parish and so please pray for me!
"Early in the morning of this day, Jesus sets out for Jerusalem, leaving Mary His Mother, and the two sisters Martha and Mary Magdalene, and Lazarus, at Bethania. The Mother of sorrows trembles at seeing her Son thus expose Himself to danger, for His enemies are bent upon His destruction; but it is not death, it is triumph, that Jesus is to receive to-day in Jerusalem. The Messias, before being nailed to the cross, is to be proclaimed King by the people of the great city; the little children are to make her streets echo with their Hosannas to the Son of David; and this in presence of the soldiers of Rome’s emperor, and of the high priests and Pharisees: the first standing under the banner of their eagles; the second, dumb with rage.
The prophet Zachary had foretold this triumph which the Son of Man was to receive a few days before His Passion, and which had been prepared for Him from all eternity. ‘Rejoice greatly, O daughter of Sion! Shout for joy, O daughter of Jerusalem! Behold thy King will come to thee; the Just and the Saviour. He is poor, and riding upon an ass, and upon a colt, the foal of an ass.’ [Zach. ix. 9]. Jesus, knowing that the hour has come for the fulfilment of this prophecy, singles out two from the rest of His disciples, and bids them lead to Him an ass and her colt, which they would find not far off. He has reached Beth phage, on Mount Olivet. The two disciples lose no time in executing the order given them by their divine Master; and the ass and the colt are soon brought to the place where He stands.
The holy fathers have explained to us the mystery of these two animals. The ass represents the Jewish people, which had been long under the yoke of the Law; the colt, upon which, as the evangelist says, no man yet hath sat [St. Mark xi. 2], is a figure of the Gentile world, which no one had ever yet brought into subjection. The future of these two peoples is to be decided a few days hence: the Jews will be rejected, for having refused to acknowledge Jesus as the Messias; the Gentiles will take their place, to be adopted as God’s people, and become docile and faithful.
The disciples spread their garments upon the colt; and our Saviour, that the prophetic figure might be fulfilled, sits upon him [Ibid. 7, and St. Luke xix. 35.], and advances towards Jerusalem. As soon as it is known that Jesus is near the city, the holy Spirit works in the hearts of those Jews, who have come from all parts to celebrate the feast of the Passover. They go out to meet our Lord, holding palm branches in their hands, and loudly proclaiming Him to be King [St. Luke xix. 38]. They that have accompanied Jesus from Bethania, join the enthusiastic crowd. Whilst some spread their garments on the way, others cut down boughs from the palm-trees, and strew them along the road. Hosanna is the triumphant cry, proclaiming to the whole city that Jesus, the Son of David, has made His entrance as her King."
-The Liturgical Year by Dom Prosper Gueranger