Heidelberg Catechism Week 28

75. Q. How does the Lord's Supper remind you and assure you that you share in Christ's one sacrifice on the cross and in all His gifts? A. In this way: Christ has commanded me and all believers to eat this broken bread and to drink this cup. With this command He gave this promise: First, as surely as I see with my eyes the bread of the Lord broken for me and the cup given to me, so surely His body was offered and broken for me and His blood poured out for me on the cross. Second, as surely as I receive from the hand of the one who serves, and taste with my mouth the bread and cup of the Lord, given me as sure signs of Christ's body and blood, so surely He nourishes and refreshes my soul for eternal life with His crucified body and poured-out-blood.

76. Q. What does it mean to eat the crucified body of Christ and to drink His poured-out blood? A. It means to accept with a believing heart the entire suffering and death of Christ and by believing to receive forgiveness of sins and eternal life. But it means more. Through the Holy Spirit, who lives both in Christ and in us, we are united more and more to Christ's blessed body. And so, although He is in heaven and we are on earth, we are flesh of His flesh and bone of His bone. And we forever live on and are governed by one Spirit, as members of our body are by one soul.

77. Q. Where does Christ promise to nourish and refresh believers with His body and blood as surely as they eat this broken bread and drink this cup? A. In the institution of the Lord's Supper: "The Lord Jesus, on the night when He was betrayed, took a loaf of bread, and when He had given thanks, he broke it and said, 'This is My body that is broken for you. Do this in remembrance of Me.' In the same way He took the cup also, after supper, saying, 'This cup is the new covenant in My blood; do this, as often as you drink it, in remembrance of Me.' For as often as you eat this bread and drink the cup, you proclaim the Lord’s death until He comes" (1 Corinthians 11:23-26). This promise is repeated by Paul in these words: "The cup of blessing that we bless, is it not a sharing in the blood of Christ? The bread that we break, is it not a sharing in the body of Christ? Because there is one bread, we who are many are one body, for we all partake of the one bread" (1 Corinthians 10:16-17).

My reflections on the reading from the book...

DeYoung sums it up better than I can:

The Lord knows our faith is weak. That's why He's given us sacraments to see, taste, and touch. As surely as you can see the bread and cup, so surely does God love you through Christ. As surely as you chew the food and drain the drink, so surely has Christ died for you. Here at the Table, the faith becomes sight. The simple bread and cup give assurance that Christ came for you, Christ died for you, Christ is coming again for you. Whenever we eat the bread and drink from the cup, we not only re-proclaim the Lord's death until He comes again (1 Cor. 11:26), we re-convince ourselves of God's provision on the cross.