On the night before he died, Christ gathered his Apostles in the upper room to celebrate the Last Supper and to give us the inestimable gift of his Body and Blood. "He did this in order to perpetuate the sacrifice of the Cross throughout the centuries until He should come again, and so to entrust to His beloved spouse, the Church, a memorial of His death and resurrection. . . ."  Thus, in the Eucharistic Liturgy we are joined with Christ on the altar of the cross and at the table of the upper room in "the sacrificial memorial in which the sacrifice of the cross is perpetuated and [in] the sacred banquet of communion with the Lord's body and blood.”  usccb.org