If there is one mystery of faith around which revolves the whole Catholic liturgy, it is the Eucharist. Christian piety has been lavish in the titles it gives to this mystery, believing it is impossible to exhaust its depth of meaning. The name "Eucharist," or thanksgiving, is to be explained either by the fact that at its institution Christ "gave thanks," or by the fact that this is the supreme act of Christian gratitude to God. Early instances of this title occur in the Teaching of the Twelve Apostles, in the letters of St. Ignatius of Antioch, and in the Apologies of St. Justin. Other familiar names are the Lord's Supper, the Table of the Lord, the Holy Sacrifice, the Holy of Holies, the Blessed Sacrament, or simply the Liturgy. Each of these and similar names concentrate on one or another of the three main aspects of the Eucharistic mystery, as Real Presence, as the Sacrifice of the Altar, or as the sacrament of Holy Communion.

In the New Testament there are four accounts of its institution, one by St. Paul in his letter to the Corinthians and three in the Synoptic Gospels of Matthew, Mark, and Luke. We have already seen how it was celebrated by the early Christian communities and from the beginning was a regular part of Christian worship.

While there is no institution narrative in John's Gospel, this is explainable by the fact that John wrote his Gospel to supplement what the other evangelists had already told. Moreover, his account of Christ's promise of the Eucharist is our most telling witness to the real bodily presence of Christ in the Blessed Sacrament.

The Catholic Catechism
Fr. John A. Hardon, S.J.