This day could be thought of as a day of contradiction. The Mass begins with the reading of Jesus’ triumphal entry into Jerusalem and His joyous reception by the crowds who strewed palm branches before Him, crying out, “Hosanna to the Son of David; blessed is he who comes in the name of the Lord; hosanna in the highest.” Today, this inspiring scene is commemorated by processions of the faithful carrying palm branches into their churches. The contradiction, however, is experienced as the full narrative of the Passion of Christ is read, culminating with Jesus’ death on the Cross.
But is it a contradiction? Is His glorious entrance into Jerusalem at the beginning of the week in any way opposed to His crucifixion? Certainly not. From a worldly perspective, for someone who lacks the ability to penetrate this mystery with the eyes of faith, the week ends in tragedy. But from the perspective of the Eternal Father, the welcome Jesus receives as He enters Jerusalem is the welcome given to the Savior of the World. His Cross would become the culmination of that act of salvation. For that reason, His entrance into that holy city was rightly celebrated with great joy, even though the people did not yet understand that the throne their new King would mount was the Cross.
As early as the fourth century, the diary of one traveler to Jerusalem records how the faithful reenacted Jesus’ triumphal entry:
And as the eleventh hour approaches, the passage from the Gospel is read, where the children, carrying branches and palms, met the Lord, saying; Blessed is He that cometh in the name of the Lord, and the bishop immediately rises, and all the people with him, and they all go on foot from the top of the Mount of Olives, all the people going before him with hymns and antiphons, answering one to another: Blessed is He that cometh in the Name of the Lord. And all the children in the neighborhood, even those who are too young to walk, are carried by their parents on their shoulders, all of them bearing branches, some of palms and some of olives, and thus the bishop is escorted in the same manner as the Lord was of old (The Pilgrimage of Etherea).
Though very few Christians are able to celebrate Passion Sunday in Jerusalem, walking from the Mount of Olives to the city gate, we are all invited to do so spiritually, meditatively, and interiorly. Our participation is not just the recalling of a historic event; it’s a real participation in that event. Our hearts must begin outside of Jerusalem’s gate today, and we must courageously and joyfully accompany our Lord into that holy city. During that first Holy Week, the people’s joy arose from their belief that Jesus would be an earthly ruler Who would free them from Roman oppression. Today, we are privileged to express our joyous acclamations as we spiritually accompany our Lord to the city of His crucifixion, because we know that Jesus’ Kingship is so much more than an earthly triumph. His triumph is an eternal one that invites us to share in His Eternity. His triumph is a sacrificial one that invites us to share in His Sacrificial Love. His triumph is a glorious one that invites us to share in the Glory of His Resurrection.
Walk with our Lord today into that holy city of Jerusalem. As you do, know that the earthly city of Jerusalem is also now a spiritual one. The events that took place there two millennia ago transcend and permeate all time. As a result, the events of Holy Week today are just as significant as they were long ago. Through the Mass, we are there. We walk with our Lord, witness all He accomplished, receive His Body and Blood sacrificed on the Cross and memorialized in the Eucharist, and are resurrected with Him on the third day. Commit yourself to this journey today, an eternal pilgrimage with our Lord to the Eternal City of Heaven.
Source: https://mycatholic.life/saints/saints-of-the-liturgical-year/palm-sunday-of-the-lords-passion