For Catholics, the Holy Eucharist / Catholic Mass is considered the most important and highest form of prayer. In fact, attending Mass is an obligation, under penalty of mortal sin, each Sunday and on certain other Holy Days of Obligation. The Mass is divided into two sections, the Liturgy of the Word and the Liturgy of the Eucharist. The Liturgy of the Word consists of two readings (one from the Old Testament and one from the New Testament), the Responsorial Psalm, the Gospel reading, the homily (or sermon), and general intercessions (also called petitions).
The center of the Mass is its second part, the Liturgy of the Holy Eucharist. During this time, Catholics share in the body and blood of Jesus in the form of the bread and wine passed out to the congregation. According to the Bible, this is done in remembrance of Christ (1 Corinthians 11:23-25; cf. Luke 22:18-20 and Matthew 26:26-28). However, according to the Catechism of the Catholic Church, paragraph 1366, "The Eucharist is thus a sacrifice because it re-presents (makes present) the sacrifice of the cross, because it is its memorial and because it applies its fruit." The catechism continues in paragraph 1367:
The sacrifice of Christ and the sacrifice of the Holy Eucharist are one single sacrifice: "The victim is one and the same: the same now offers through the ministry of priests, who then offered himself on the cross; only the manner of offering is different." "And since in this divine sacrifice which is celebrated in the Mass, the same Christ who offered himself once in a bloody manner on the altar of the cross is contained and is offered in an unbloody manner . . . this sacrifice is truly propitiatory."
In the book of Malachi, the prophet predicts elimination of the old sacrificial system and the institution of a new sacrifice: "I have no pleasure in you, says the Lord of hosts, and I will not accept an offering from your hand. For from the rising of the sun to its setting my name will be great among the nations, and in every place incense will be offered to my name, and a pure offering. For my name will be great among the nations, says the Lord of hosts" (Malachi 1:10-11). This means that God will one day be glorified among the Gentiles, who will make pure offerings to Him in all places. The Catholics see this as the Eucharist. However, the apostle Paul seems to have a different slant on it: "I appeal to you therefore, brothers, by the mercies of God, to present your bodies as a living sacrifice, holy and acceptable to God, which is your spiritual worship" (Romans 12:1). The Eucharist can only be offered in select places: churches consecrated and blessed according to Catholic canon law. The idea of offering our bodies as living sacrifices fits better with the language of the prediction, which says that the sacrifices will be offered "in every place."
The Roman Catholic Church believes that the bread and wine of the Holy Eucharist become the actual body and blood of Jesus. They attempt to support their system of thought with passages such as John 6:32-58; Matthew 26:26; Luke 22:17-23; and 1 Corinthians 11:24-25. In A.D. 1551, the Counsel of Trent officially stated, "By the consecration of the bread and wine there takes place a change of the whole substance of the bread into the substance of the body of Christ our Lord and of the whole substance of the wine into the substance of his blood. This change the holy Catholic Church has fittingly and properly called transubstantiation" (Session XIII, chapter IV; cf. canon II). By sharing in the Eucharistic meal, the Church teaches that Catholics are fulfilling John 6:53: "Truly, truly, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you."
What does that really mean? Jesus goes on to say that "it is the Spirit who gives life; the flesh is of no avail. The words that I have spoken to you are spirit and life" (John 6:63-64). So, if "the flesh is of no avail," why would we have to eat Jesus’ flesh in order to have eternal life? It does not make sense, until Jesus tells us that the words He speaks are "spirit." Jesus is saying that this is not a literal teaching, but a spiritual one. The language ties in perfectly with the aforementioned statement of the apostle Paul: "Present your bodies as a living sacrifice, holy and acceptable to God, which is your spiritual worship" (Romans 12:1).
In Jewish thought, bread was equated with the Torah, and "eating of it" was reading and understanding the covenant of God (cf. Deuteronomy 8:3). For example, the apocryphal book of Sirach states, "'He who eats of me will hunger still, he who drinks of me will thirst for more; he who obeys me will not be put to shame, he who serves me will never fail.' All this is true of the book of Most High’s covenant, the law which Moses commanded us as an inheritance for the community of Jacob" (Sirach 24:20-22). Quoting from Sirach here is not endorsing it as Scripture; it only serves to illustrate how the Jewish people thought of Mosaic Law. It is important to understand the equating of bread with the Torah to appreciate Jesus’ real point.
In John 6, Jesus is actually telling the crowd that He is superior to the Torah (cf. John 6:49-51) and the entire Mosaic system of Law. The passage from Sirach states that those who eat of the Law will "hunger still" and "thirst for more"; this language is mirrored by Jesus when He says, "He who comes to Me will never be hungry, he who believes in Me will never be thirsty" (John 6:35). Jesus is not commanding people to literally eat His flesh and drink His blood. He is telling them the core of all Christian doctrine: belief in Jesus Himself ("The work of God is this: to believe in the One He has sent," John 6:29, emphasis added). Therefore, the Catholic interpretation of John 6 is unbiblical.
Second, there is a very clear analogy in John 6 to the days of Moses and the eating of manna. In the days of Moses, manna was God’s provision for food for the Israelites as they wandered in the wilderness. In John 6, however, Jesus claimed to be the true manna, the bread of heaven. With this statement Jesus claimed to be God’s full provision for salvation. Manna was God’s provision of deliverance from starvation. Jesus is God’s provision of deliverance from damnation. Just as the manna had to be consumed to preserve the lives of the Israelites, so Jesus has to be consumed (fully received by faith) for salvation to be received.
It is very clear that Jesus referred to Himself as the Bread of Life and encouraged His followers to eat of His flesh in John 6. But we do not need to conclude that Jesus was teaching what the Catholics have referred to as transubstantiation. The Lord’s Supper / Christian communion / Holy Eucharist had not been instituted yet. Jesus did not institute the Holy Eucharist / Mass / Lord’s Supper until John chapter 13. Therefore, to read the Lord’s Supper into John 6 is unwarranted. As suggested above, it is best to understand this passage in light of coming to Jesus, in faith, for salvation. When we receive Him as Savior, placing our full trust in Him, we are “consuming His flesh” and “drinking His blood.” His body was broken (at His death) and His blood was shed to provide for our salvation. 1 Corinthians 11:26, “For whenever you eat this bread and drink this cup, you proclaim the Lord’s death until He comes.”
Whether the Catholic definition of Holy Eucharist is a "re-sacrifice" of Christ, or a "re-offering" of Christ’s sacrifice, or a “re-presentation” of Christ’s sacrifice, the concept is unbiblical. Christ does not need to be re-sacrificed. Christ’s sacrifice does not need to be re-offered or re-presented. Hebrews 7:27 declares, "Unlike the other high priests, He (Jesus) does not need to offer sacrifices day after day, first for his own sins, and then for the sins of the people. He sacrificed for their sins ONCE for all when He offered Himself." Similarly, 1 Peter 3:18 exclaims, "For Christ died for sins ONCE for all, the righteous for the unrighteous, to bring you to God..." Christ’s once-for-all death on the cross was sufficient to atone for all of our sins (1 John 2:2). Therefore, Christ’s sacrifice does not need to be re-offered. Instead, Christ’s sacrifice is to be received by faith (John 1:12; 3:16). Eating Christ’s flesh and drinking His blood are symbols of fully receiving His sacrifice on our behalf, by grace through faith.