Lord's Day 29

Q. 78.  Do then the bread and wine become the very body and blood of Christ?
A.  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;1 so the bread in the Lord’s Supper is not changed into the very body of Christ,2 though agreeably to the nature and properties of sacraments,3 it is called the body of Christ Jesus.

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”?
A.  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;4 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;5 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.6