Q. 78. Do then the bread and wine become the very body and blood of Christ?
Not at all: but as the water in baptism is not changed into the blood of Christ, neither is the washing away of sin itself, being only the sign and confirmation thereof appointed of God; so the bread in the Lord’s Supper is not changed into the very body of Christ; though agreeably to the nature and properties of sacraments, it is called the body of Christ Jesus.
 1 Corinthians 10:1–4; 1 Peter 3:21; John 6:35, 62–63;  1 Corinthians 10:16, &c., and 11:20, &c.;  Genesis 17:10–11, 14; Exodus 12:26–27, 43, 48; Acts 7:8; Matthew 26:26; Mark 14:24.
Q. 79. Why then doth Christ call the bread His body, and the cup His blood, or the new covenant in His blood; and Paul the “communion of the body and blood of Christ”?
Christ speaks thus, not without great reason, namely, not only thereby to teach us, that as bread and wine support this temporal life, so His crucified body and shed blood are the true meat and drink, whereby our souls are fed to eternal life; but more especially by these visible signs and pledges to assure us, that we are as really partakers of His true body and blood (by the operation of the Holy Ghost) as we receive by the mouths of our bodies these holy signs in remembrance of Him; and that all His sufferings and obedience are as certainly ours, as if we had in our own persons suffered and made satisfaction for our sins to God.
 John 6:51, 55–56;  1 Corinthians 10:16–17 and 11:26–28; Ephesians 5:30;  Romans 5:9, 18–19 and 8:4.
In the same night wherein the Lord Jesus was betrayed, He instituted the Lord’s Supper by taking bread, breaking it and giving it to His disciples, saying: “Take, eat: this is my body, which is broken for you: this do in remembrance of me” (1 Cor 11:24; cf. Mt 26:26; Mk 14:22). And then He took the cup and said: “this is my blood of the new testament, which is shed for many for the remission of sins” (Mt 26:28; 1 Cor 11:25). Most of us reading these words of the Lord, would no doubt know intuitively that the Lord was speaking in a figure. He could not mean that the bread actually becomes His flesh and the wine actually becomes His blood. Yet, this is actually what Roman Catholicism teaches in her repugnant doctrine known as transubstantiation. And this is the reason why every Protestant creed arising from the Reformation times makes mention that the bread and wine do not become the actual body and blood of Christ.
To be fair to Rome, however, we must admit that certain somewhat enigmatic statements in Scripture, could have led her theologians to believe against reason that transubstantiation is biblical. Did not the Lord say: “For my flesh is meat indeed, and my blood is drink indeed. He that eateth my flesh, and drinketh my blood, dwelleth in me, and I in him” (Jn 6:55–56)? And did not the Apostle Paul ask: “The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ?” (1 Cor 10:16)? How should we understand these statements?
Q. 79 teaches us that we understand them in terms of the sacramental union between the elements and the spiritual realities that they represent. That is to say, there is such a close connection between the elements and their spiritual reality that when we, by faith, partake of the bread and wine physically, we partake of the body and blood of Christ spiritually. As the bread and wine nourish us physically, so the crucified body and shed blood of Christ nourish us spiritually when we partake the bread and wine by faith. But the bread and wine are not the flesh and blood of Christ. Eating the bread and wine without discerning and believing what they represent is not only without value, but spiritually hazardous (1 Cor 11:29). Doing so would in some ways be like eating a handbill advertising some delicious pizza! The purpose of the handbill is to make you salivate and head for a pizzeria; it serves no more than that. The elements of the Lord’s Supper are intended also to point us to Christ, to hunger and thirst after Him, but there is also a sacramental union between the elements and the spiritual reality so that if we partake by faith, we have the assurance that Christ will grant us the spiritual benefits pointed to by the elements, namely union with Him.
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