Heidelberg Catechism – Lord’s Day 29
Q. Do the bread and wine become the very body and blood of Christ?
A. No, for as the water in baptism is not changed into the blood of Christ, nor becomes the washing away of sins by itself, but is only a divine sign and confirmation of it, so also in the Lord’s Supper the sacred bread does not become the body of Christ itself, although, in accordance with the nature and usage of sacraments, it is called the body of Christ.
Q. Then why does Christ call the bread his body, and the cup his blood, or the New Covenant in his blood, and why does the apostle Paul call the Supper “a means of sharing” in the body and blood of Christ?
A. Christ does not speak in this way except for a strong reason. He wishes to teach us by it that as bread and wine sustain this temporal life so his crucified body and shed blood are the true food and drink of our souls for eternal life. Even more, he wishes to assure us by this visible sign and pledge that we come to share in his true body and blood through the working of the Holy Spirit as surely as we receive with our mouth these holy tokens in remembrance of him, and that all his sufferings and his death are our own as certainly as if we had ourselves suffered and rendered satisfaction in our own persons.