What is "the food that endures" ?
In other words, this physical world is like a facade or perverted reflection of the spiritual realm. It is like looking at a pond's reflection of a tree on the other side of the pond. Just consider this reflection. Does the reflection look like the tree? Yes, But is the reflection the tree? No. Furthermore, the reflection of the tree on the pond is upside down, with the leaves at the bottom.
This is much like the difference between the physical and the spiritual realm, because all life comes from the spiritual realm - and each of us is from the spiritual realm. But since we are animating these physical bodies, life is only portrayed proximally within the physical world.
One might compare this to a movie set. The movie set is not permanent, nor is it real in that it is just made up to make the movie look like it is real. The movie set might look like a real life scene but it is not. It is a facade of a real life scene.
Jesus is not claiming to be God here. He states: "On him God the Father has placed His seal of approval.” How much clearer can this be? He is clearly showing that he and God are distinct individuals. In order for someone to place their “seal of approval” on someone else there must be two distinct individuals. For one individual to approve another individual, there must be one person who approves, and another person who is approved.
It is not as if Jesus is the Supreme Being and God needs to create a fake approval process to boost Himself. God does not need anyone's seal of approval. But Jesus is clearly illustrating that he has received such a seal of approval - as he has been empowered by the Supreme Being to deliver God’s message to these people.
And the "oneness" that Jesus once indicated between himself and God is their unity of purpose: Jesus does God's will, so there is a oneness of purpose. God has given Jesus His “seal of approval” because Jesus is carrying out God's will. This means that Jesus' teachings and activities represents the wishes of the Supreme Being. Jesus said this specifically:
"For I have come down from heaven not to do my will but to do the will of Him who sent me." (John 6:38)and
"My teaching is not my own. It comes from the One who sent me." (John 7:16)With Jesus' statement above, he is also indicating that he is empowered to deliver people back to God ("give you"). And how does Jesus give them the "food that endures to eternal life"?
By his teachings. If they (and we) listen to and apply Jesus' teachings, they (and we) can receive what he gives, and be saved.
Being saved is not an automatic process by which we simply say "I surrender to Jesus" and then we are saved. It is not as if Jesus' "dying" on the cross automatically saves anyone. We must apply Jesus' teachings. It is following Jesus' teachings that saves us. And what was his primary teaching?
“ ‘Love the Lord your God with all your heart and with all your soul and with all your mind.' This is the first and greatest commandment.” (Matt. 22:37-38)