"I have food to eat that you know nothing about." (John 4:32)

Here Jesus is responding to his disciples, who urged him to eat:
“Rabbi, eat something.” (John 4:31)
Jesus responded that he is eating another type of food:

Spiritual food

This statement also confirms the meaning of “give us each day our daily bread” (Luke 11:3) in the Lord’s prayer. The food that Jesus is discussing is the food that feeds the spiritual self.

Our real food is a loving relationship with the Supreme Person, God. Once the spirit-person within - the spiritual being - renews their relationship with the Supreme Being, they want to do the will of the One they love:

Such a person will want to do God's will out of love. This service relationship satisfies the spiritual person, just as physical food satisfies the physical body’s hunger.

And why does Jesus say that his audience knows nothing about this spiritual food? It is because the physical world is where those who don't want to have a relationship with God come to. This is where those who have rejected their relationship with God go.

This issue of internal satisfaction is specifically why most people in the physical world are struggling to become fulfilled with the forms and things of the physical world, yet remain empty and unhappy.

Full yet empty within

This is why even the richest and most glorified people—rock stars like Michael Jackson, Elvis Presley and so many movie stars, descend into depression, drug abuse and suicidal behavior. Even though they had everything material a person could ever desire: The adoration of millions, and all the money they could ever spend; they are still empty. They were still unfulfilled despite having everything most of us dream of having.

This points to the reality that we are not these physical bodies. If we were these physical bodies, then why would the things of the physical world not satisfy us?

Since the forms and things of the physical world do not satisfy us, we must not be physical. We must have a deeper existence, one beyond the confines of this temporary physical body.

And certainly, we see this at the time of death. A dead body lies there, but without life. The entire body - every molecule and cell - is still there in the dead body. But the body is lifeless. What has changed?

The spirit-person within - who was driving that physical body - has left.

The fact that we cannot see this spirit-person within who leaves the physical body points to the fact that the spirit-person lies within another dimension. It is not perceivable by the gross physical senses.

This is why there are so many clinical death cases where a person whose body was revived reports having left the body and observed things from outside the body. They observed the body from above, and many cases prove the spirit-person could observe things that were not otherwise observed as their physical body lay with closed eyes and a sheet over the head.

Since we are spiritual in essence and not these physical bodies, then we cannot be satisfied by the things of the physical world. It might be compared to a driver of a car being hungry and thinking that if he fills his car's gas tank up with gas he will no longer be hungry. He will soon find that filling the gas tank won't relinquish the car driver's hunger because the car driver is not the car.

For this reason, Jesus, identifying himself as the spiritual child of God and not the physical body, relayed to his students that his food was loving the Supreme Being and serving Him. This is confirmed by a similar statement to come:
“My food,” said Jesus, “is to do the will of Him who sent me and to finish His work." (John 4:34)