What did Jesus mean when He said we must eat His flesh and drink His blood? After Jesus crossed to Capernaum, those who had been fed came looking for Him, asking, “Rabbi, why did you come here?” (v 25). We start getting to the heart of the matter when Jesus said, “Do not labor for the food which perishes, but for the food which endures to everlasting life, which the Son of Man will give you” (v 27).
The Jews understood Jesus to be commanding them to labor (do a work) by which they could have the everlasting food of which Jesus just spoke. Jesus says faith in Him is the key to receiving this everlasting food (vv 28-29). The Jews then ask for a sign by which they could believe in Him, despite Jesus’ statement in John 5:36 that His works bear testimony to His claims, as does the Old Testament (John 5:39). Note Jesus’ statement in John 5:38, “But you do not have His word abiding in you, because whom He sent, Him you do not believe.” And John 5:40 – “You would not come to me that you might have life.” Jesus is clear that faith in Him as the Son of God is the key to everlasting life.
Jesus identifies Himself as “the true bread from heaven” and “the bread of God… who came down from heaven and gives life to the world” (vv 32-33). In v 34, the Jews again request this bread. So Jesus again identifies Himself as the source of life, saying, “I am the bread of life. He who comes to Me shall never hunger, and he who believes in Me shall never thirst” (v 35). In verse 40 Jesus says, “And this is the will of Him who sent Me, that everyone who sees the Son and believes in Him may have everlasting life; and I will raise him up at the last day.”
So we see a pattern of faith in Jesus as being equated to: 1) possessing the food which endures unto eternal life (v 27); 2) possessing the bread of God which gives life (v 33); 3) never hungering or thirsting (v 35); and 4) having everlasting life and being raised in the last day (v 40).
Read vv 47-50 again. Here, possessing faith in Jesus is the same as eating the bread of life which comes down from heaven. In the first instance, one who believes in Jesus has everlasting life, and in the second he who eats of the bread will not die = the same thing.
In light of all this, verses 51-58 are not so much of a mystery. It is also good to note that this eating flesh and drinking blood are not a reference to the Lord’s Supper.