The holy Eucharist completes Christian initiation. Those who have been raised to the dignity of the royal priesthood by Baptism and configured more deeply to Christ by Confirmation participate with the whole community in the Lord's own sacrifice by means of the Eucharist. (Catechism of the Catholic Church, #1322)
"At the Last Supper, on the night he was betrayed, our Savior instituted the Eucharistic sacrifice of his Body and Blood. This he did in order to perpetuate the sacrifice of the cross throughout the ages until he should come again, and so to entrust to his beloved Spouse, the Church, a memorial of his death and resurrection: a sacrament of love, a sign of unity, a bond of charity, a Paschal banquet ‘in which Christ is consumed, the mind is filled with grace, and a pledge of future glory is given to us.'" (Catechism of the Catholic Church, #1323)
"The sacrificial nature of the Mass, solemnly asserted by the Council of Trent in accordance with the Church's universal tradition, was reaffirmed by the Second Vatican Council, which offered these significant words about the Mass: 'At the Last Supper our Savior instituted the Eucharistic Sacrifice of his Body and Blood, by which he would perpetuate the Sacrifice of the Cross throughout the centuries until he should come again, thus entrusting to the Church, his beloved Bride, the memorial of his death and resurrection.'" (General Instruction of the Roman Missal, #2)
Information on Changes to the Mass (to be implemented the First Sunday of Advent 2011)