A sacrifice is a ritual offering made to God by a priest on behalf of the people, as a sign of adoration, gratitude, supplication, and communion. The perfect sacrifice was Christs death on the cross; by this sacrifice, Christ accomplished our redemption as high priest of the new and eternal covenant. The sacrifice of Christ on the cross is commemorated and mysteriously made present in the Eucharistic sacrifice of the Church.
All who believe in the real presence and believe the mass (divine liturgy) to be a re-presentation of the sacrifice of our Lord, Jesus Christ, on the cross carry out the command of the Lord by celebrating the memorial of his sacrifice. In so doing, they offer to the Father what he has himself given to them: the gifts of his creation, bread and wine which, by the power of the Holy Spirit and by the words of Christ, have become the body and blood of Christ. Christ is thus really and mysteriously made present.
Those who hold to this faith believe that everything that the priesthood of the Old Covenant prefigured finds its fulfillment in Christ Jesus, the one mediator between God and men. Christian tradition considers Melchizedek, priest of God Most High, as a prefiguration of the priesthood of Christ, the unique high priest after the order of Melchizedek; holy, blameless, unstained, by a single offering he has perfected for all time those who are sanctified, that is, by the unique sacrifice of the cross.
The redemptive sacrifice of Christ is unique, accomplished once for all; yet it is made present in the Eucharistic sacrifice of the Church. The same is true of the one priesthood of Christ; it is made present through the ministerial priesthood without diminishing the uniqueness of Christs priesthood: Only Christ is the true priest, the others being only his ministers.