82 By means of the Eucharistic Sacrifice Christ our Lord willed to give the faithful a striking manifestation of our union among ourselves and with our divine Head, wonderful as it is and beyond all praise. For in this Sacrifice the sacred minister acts as the viceregent not only of our Savior but of the whole Mystical Body and of each one of the faithful. In this act of Sacrifice through the hands of the priest, by whose word alone the Immaculate Lamb is present on the altar, the faithful themselves, united with him in prayer and desire, offer to the Eternal Father a most acceptable victim of praise and propitiation for the needs of the whole Church. And as the Divine Redeemer, when dying on the Cross, offered Himself to the Eternal Father as Head of the whole human race, so "in this clean oblation" He offers to the heavenly Father not only Himself as Head of the Church, but in Himself His mystical members also, since He holds them all, even those who are weak and ailing, in His most loving Heart.
Source: Mystici Corporis Christi (Vatican.va)