Question 47: Does the Lord's Supper add anything to Christ's atoning work?
Answer: No, Christ died once for all. The Lord's Supper is a covenant meal celebrating Christ's atoning work; it is also a means of strengthening our faith as we look to him, and a foretaste of the future feast. But those who take part with unreprentant hearts eat and drink judgment on themselves.
Not only does the Catholic teaching of the Lord's Supper as a re-presentation of Christ's sacrifice contradict the biblical teaching of the sufficiency of his once-for-all sacrifice on the cross, it also contradicts the biblical teaching of the sufficiency of his high priesthood for us. In the Catholic teaching, Jesus Christ is our high priest, but we also need the mediatorial work of lesser priests, officers of the church, who are uniquely qualified to present the sacrifice of the mass to God repeatedly. The Catholic teaching imports an old covenant reality (a distinct earthly priesthood among God's people) into the new covenant, where it does not belong.
Scripture clearly teaches that the priesthood of Aaron, the first high priest of Israel (known as the "Levitical priesthood" because Aaron was of the tribe of Levi) has now passed away with the inauguration of the new covenant. In this new covenantal arrangement, Jesus Christ, of the tribe of Judah (not Levi) is now the one Mediator between God and men (1 Tim. 2:5). His qualifications for the priesthood are not tied to his genealogical descent, but he is rather appointed to this task in the order of Melchizedek (Hebrews 7), a far superior priesthood than that of Aaron. And because Christ is our one high priest, and we are united to him by faith, that makes all who are in Christ "a royal priesthood" (1 Pet. 2:9), a community of priest-kings who share equal access to God. In the church, we do not depend on a priestly class of men to mediate our relationship with God. We depend on Christ alone. And the Lord's Supper bears witness to that by calling us to remember his high priestly work of atonement and intercession for us.
Suggested passage for personal or family reading: Hebrews 7. What are the various arguments the author makes about how Jesus Christ is a greater priest than any of the Levitical priests? How does the argument of this passage demonstrate that the Catholic teaching on the priesthood has major errors?