Do then the bread and wine become the very body and blood of Christ?
Not at all. Just as the water in baptism is not changed into the blood of Christ and is not itself the washing away of sin, but only its God-appointed sign and confirmation, so the bread in the Lord’s Supper is not changed into Christ’s actual body. Yet it is called the body of Christ in keeping with the nature and properties of sacraments.
Why does Christ call the bread His body and the cup His blood, or the new covenant in His blood, and why does Paul speak of communion in Christ’s body and blood?
Christ speaks thus for good 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 food and drink by which our souls are fed to eternal life, but more especially by these visible signs and pledges to assure us that we are as really sharers in His true body and blood by the operation of the Holy Spirit 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.