John 6:47-51 — Verily, verily, I say unto you, He that believeth on Me hath everlasting life.
I am that bread of life.
Your fathers did eat manna in the wilderness, and are dead.
This is the bread which cometh down from heaven, that a man may eat thereof, and not die.
I am the living bread which came down from heaven: if any man eat of this bread, he shall live for ever: and the bread that I will give is My flesh, which I will give for the life of the world.
Manna kept the Jews fed in the wilderness, but those who ate it eventually died. The bread of life enables men to live forever. Manna didn't even get the fathers into the promised land because they would not believe.
Bread that I will give — referring to Jesus' death. It is His flesh, His body. The bread is not Jesus' teaching or His example.
hath eternal life — present tense — not a future event
eat — assimilate it, make it part of one's life.
dead (verse 49) — physically
die (verse 50) — spiritually
"I am that bread of life" (6:48). This is the first of the seven "I am" titles of Christ found in this Gospel, and found nowhere else. The others are, "I am the light of the world" (8:12); "I am the door" (10:9); "I am the good shepherd" (10:11); "I am the resurrection and the life" (11:35); "I am the way, the truth, and the life" (14:6); "I am the true vine" (15:1). They all look back to that memorable occasion when God appeared to Moses at the burning bush, and bade him go down into Egypt, communicate with His people, interview Pharaoh, and command him to let the children of God go forth into the wilderness to worship Jehovah. And when Moses asked, Who shall I say hath sent me?, the answer was, "Thus shalt thou say unto the children of Israel, I AM hath sent me unto you" (Exodus 3:14). Here in John, we have a sevenfold filling out of the "I am" — I am the bread of life, etc. Christ's employment of these titles at once identifies Him with the Jehovah of the Old Testament, and unequivocally demonstrates His absolute Deity. — Exposition of the Gospel of John, by Arthur W. Pink, page 341.