With the evening Mass of Holy Thursday begins the Sacred Triduum, the most solemn celebration of the liturgical year. The Church commemorates the Last Supper, at which Our Lord Jesus Christ, before His Passion, instituted the Sacrament of His Body and Blood, established the priesthood of the New Covenant, and gave His disciples the commandment of charity. The joy of the institution of the Eucharist is already overshadowed by the nearness of the Passion. After Mass the Blessed Sacrament is carried to the altar of repose, and the Church keeps watch with her Lord in the night. Thus begins the one great mystery of the Triduum, extending from the Supper to the Cross, and from the Cross to the Resurrection.
The Church, which since the first days of Lent has prepared the faithful for the commemoration of the Passion of the Redeemer, now enters upon the holiest days of the year. The love of Christ is manifested on this evening in its fullness. The Son of God, knowing that His hour had come to pass out of this world to the Father, and having loved His own who were in the world, loved them unto the end. He gathers them in the supper room. There, before delivering Himself to His enemies, He gives them the greatest pledge of His love. He institutes the Sacrament of His Body and Blood. The bread becomes His Body, the wine becomes His Blood. He gives Himself to them, that He may remain with them, not only in memory, but in reality. He wills that this divine gift should continue to the end of time. Therefore He gives to the Apostles and their successors the power to do what He Himself has done. On this evening the priesthood of the New Covenant is instituted, together with the sacrifice they are to offer.
But the love of the Redeemer does not stop at this divine gift. He also wills to give the example of humility. He rises from the table, lays aside His garments, girds Himself with a linen cloth, and begins to wash the feet of His disciples. The Lord and Master bows before His servants. He who has all power in heaven and on earth performs the task of a servant. Peter at first refuses, but the Lord answers, If I wash thee not, thou shalt have no part with Me. Thus He teaches that the way to share in His mysteries is the way of humility. After He has washed their feet He says, If I then, your Lord and Master, have washed your feet, you also ought to wash one another’s feet. Thus He gives to His Church the commandment of love, which gives this day its name, Mandatum novum do vobis, that you love one another as I have loved you.
After the Supper the Lord leaves the room and goes to the garden of Olives. The Church follows Him in spirit. But before following Him, she preserves with reverence the Blessed Sacrament. The sacred hosts are carried to a separate place. There the Lord remains present in the silence of the night. The faithful keep watch with Him. They remember the sorrow of the Redeemer and His words to the Apostles, remain here and watch with Me. The altar is stripped. The lights are extinguished. Everything proclaims that the hour of the Passion is near. The Church is silent, yet she remains with her Lord. Thus ends this holy evening, in which the love of Christ has been manifested in the Sacrament, in the priesthood, in humility, and in the silent presence that remains until the day of the Cross. (Dom Prosper Guéranger)