“Amen, amen I state to you, the one believing has eternal life. I myself am the bread of the life. Your fathers ate the manna in the wilderness and they died. This is the bread descending from the sky in order that anyone may eat out of it and may not die.”
The BC 1350 “manna in the wilderness” was not really the “bread of life”. It really pointed to Jesus himself. And the “life” the manna gave only maintained life for a time. The real “bread of life” means no death, ever.
“I myself am the living bread that descended from the sky. If anyone may eat out of this bread, he will live into eternity and in fact the bread that I myself will give on behalf of the life of the world is my flesh.”
Eaters of “the living bread”, come down with heaven’s life, may live into eternity. Jesus will give his "own flesh" for them. Even those who will have killed him will be able to live because he will have died in their place.
So the Judeans were arguing towards themselves, stating, “How is this one able to give us his flesh to eat?” So Jesus said to them, “Truly, truly I state to you, unless you may eat the flesh of the Son of Man and may drink his blood, you do not have life in yourselves. The one consuming my flesh and drinking my blood has eternal life and I will raise him up in the last day. Because my flesh is true food, and my blood is true drink.”
Jesus continues the metaphor with a startling truth. “Unless you may eat the flesh of the Son of Man and may drink his blood, you do not have life in yourselves.” No person has heaven’s life without eating the “bread of life”.
“The one consuming my flesh and drinking my blood stays in me and I in him. Just as he sent me out, the living Father, and I am living through the Father, so the one consuming me—that one will live through me.”
It seems that there will be some (perhaps many) who will only purport to partake of Jesus. They will not “stay in him” nor he in them. The truth is that only those who “stay in him” will truly be “consuming his flesh and drinking his blood”. In fact, those - only - will “live through him”. That is very clear.