How does the Lord’s Supper instruct and assure you that you share in Christ’s one sacrifice on the cross and all His benefits?
Thus: that Christ has commanded me and all believers to eat of this broken bread and to drink of this cup in remembrance of Him, adding these promises: first, that His body was offered and broken on the cross for me and His blood shed for me as certainly as I see with my eyes the bread of the Lord broken for me and the cup communicated to me; and further, that He feeds and nourishes my soul to everlasting life with His crucified body and shed blood as assuredly as I receive from the hands of the minister and taste with my mouth the bread and cup of the Lord as certain signs of the body and blood of Christ.
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What is it then to eat the crucified body and drink the shed blood of Christ?
It is not only to embrace with believing heart all the sufferings and death of Christ and thereby to obtain the pardon of sin and life eternal, but also, besides that, to become more and more united to His sacred body by the Holy Spirit who dwells both in Christ and in us, so that we, though Christ is in heaven and we on earth, are nevertheless flesh of His flesh and bone of His bone, and that we live and are governed forever by one Spirit as members of the same body are by one soul.
Where has Christ promised that He will as certainly feed and nourish believers with His body and blood as they eat of this broken bread and drink of this cup?
In the institution of the supper which is expressed in these words: The Lord Jesus, on the night when He was betrayed, took bread, and when He had given thanks He broke it and said: Take, eat; this is My body which is broken for you; this do in remembrance of Me. After the same manner also He took the cup after He had eaten, saying: This cup is the new covenant in My blood; this do, as often as you drink it, in remembrance of Me. For as often as you eat this bread and drink this cup you show the Lord's death until He comes.
This promise is repeated by the holy apostle Paul where he says: 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? For we, though many, are one bread and one body, for we are all sharers in that one bread.