The Triumphal Procession: Hosanna in the Highest
At Jerusalem, in the fourth century, on the very spot where the Palm procession took place, the Gospel narrative was read in which we see Christ, hailed as King of Israel and taking possession of His capital, Jerusalem, which is really no more than the type of Jerusalem above. After this, a bishop, mounted on an ass, rode up to the Church of the Resurrection surrounded by a multitude carrying palms and singing anthems and hymns.
The Church of Rome, it would seem, adopted this practice about the ninth century and added to it the rite for the Blessing of the Palms. In this benediction the Church prays for health of mind and body for those who dwell in houses where the palms are preserved.
This procession is composed of the faithful, who with palm in hand and songs of Hosanna on their lips, proclaim Christ's Kingship every year, throughout the whole world and in all generations. At the Easter Feast they will be united to this glorious Victor through the Sacraments. It is this that is represented by the procession when it stops at the door of the Church, into which some members of the choir have already found their way. They chant alternately with the clergy, hailing the King of Glory each in his turn. Soon the door opens after the cross has knocked on it three times and the procession enters the church; so does the Cross of Christ open heaven to us and so will the elect one day enter with their Lord into eternal glory.
We should keep a blessed palm carefully in our home. It is a sacramental which will obtain for us graces in virtue of the Church's prayer and strengthen our faith in Christ, who full of mercy, symbolized by the olive branch whose oil soothes our wounds, has conquered sin, death and the devil in a victory of which these sacred palms are the type.
Source: Dom Gaspar Lefebvre, OSB, 1945, adapted and abridged.