Did the Apostles who took part in the Last Supper understand the meaning of the words spoken by Christ? Perhaps not. Those words would only be fully clear at the end of the Triduum sacrum, the time from Thursday evening to Sunday morning. Those days embrace the mysterium paschale; they also embrace the mysterium eucharisticum.
The Church was born of the paschal mystery. For this very reason the Eucharist, which is in an outstanding way the sacrament of the paschal mystery, stands at the centre of the Church’s life. This is already clear from the earliest images of the Church found in the Acts of the Apostles: “They devoted themselves to the Apostles’ teaching and fellowship, to the breaking of bread and the prayers” (2:42). The “breaking of the bread” refers to the Eucharist. Two thousand years later, we continue to relive that primordial image of the Church. At every celebration of the Eucharist, we are spiritually brought back to the paschal Triduum: to the events of the evening of Holy Thursday, to the Last Supper and to what followed it. The institution of the Eucharist sacramentally anticipated the events which were about to take place, beginning with the agony in Gethsemane. Once again we see Jesus as he leaves the Upper Room, descends with his disciples to the Kidron valley and goes to the Garden of Olives. Even today that Garden shelters some very ancient olive trees. Perhaps they witnessed what happened beneath their shade that evening, when Christ in prayer was filled with anguish “and his sweat became like drops of blood falling down upon the ground” (cf. Lk 22:44). The blood which shortly before he had given to the Church as the drink of salvation in the sacrament of the Eucharist, began to be shed; its outpouring would then be completed on Golgotha to become the means of our redemption: “Christ… as high priest of the good things to come…, entered once for all into the Holy Place, taking not the blood of goats and calves but his own blood, thus securing an eternal redemption” (Heb 9:11- 12). — from Ecclesia De Eucharistia (2003)