"If I testify about myself, my testimony is not true." (John 5:31-32)

"If I testify about myself, my testimony is not true. There is another who testifies in my favor, and I know that His testimony about me is true." (John 5:31-32) 

Why isn't Jesus' testimony true if he testifies about himself?

Jesus is continuing to answer to those who questioned his working on the Sabbath. Note the point being made just prior to this statement:
“By myself I can do nothing; I judge only as I hear, and my judgment is just, for I seek not to please myself but Him who sent me.” (John 5:30)
Jesus is working to please the Supreme Being. He is God's servant and seeks to please God by doing His will.

Now Jesus is talking about testimony. Just as Jesus worked to please the Supreme Being; God supports Jesus by giving him the testimony needed.

Jesus is referring to a relationship with God. It is not as if the Supreme Being is some sort of monolith that is being served by Jesus. God is not a vague cloud or burning bush. God is a Person, and Jesus is relating to, and representing that Person. Of course, God is also going to testify for Jesus and support Jesus.

Speaking of monoliths, clouds, or burning bushes: It is interesting how some people envision not only God but heaven or the spiritual world in general.

If they don't think of the Supreme Being as a monolith, cloud or burning bush, many imagine God as an old man in a long white beard. Why is that? Because they think that since God is the Original Being, they think He must be really old.

All of these imaginings are placing the Supreme Being within the confines of our mental speculation and the rules of the physical world. God is completely spiritual, and outside the scope of our minds. He is also not bound by the restrictions of the physical world. 

God is the Original Being. There is no aging in the spiritual dimension. God never ages. He is ever-youthful and ever-beautiful. And we are eternal as well.

Is heaven in the clouds?

Many also see the spiritual world as a place where old-looking people sit on clouds and play the harp all day. Some depict heaven as a place where we sit in lounge chairs sipping lemonade. They think of heaven to be like retirement. This sure seems like a boring life for the rest of eternity. Furthermore, most of the depictions of heaven by ecclesiastical sects exclude God. How can you have heaven without the Supreme Being?

Such speculative journeys utilize mental speculation within the confines of the physical world to imagine a dimension that is outside the realm of the physical world.

These imaginings are flawed in that they are founded upon false identification. They consider the physical body to be me: That I am this body. This is despite the fact that every physical body dies and decomposes. We know this from seeing remains.

This does not mean that there is no activity and no forms in the spiritual world, however. The spiritual world is full of activity, play and relationships; and each living being, including the Supreme Being, has form. The forms of the spiritual world are free of disease and aging, however. They are free from the temporary nature of the physical world - a place of pain, disease, and death.

What is Jesus testifying about?

Jesus is giving a testimony about God. The spiritual dimension is full of loving relationships and activity. And the Supreme Being is the focus and center of those loving relationships. This is because the Supreme Being is the most attractive person in the spiritual world. Therefore, He is the center of all activity in the spiritual world, and everyone is completely fulfilled in their relationship with Him.

This is the place Jesus wants us to return to. This is our home. This is that perfect place we are always striving for on earth (but the earth will never be). It is a place where everyone is happy because everyone in the spiritual realm has a personal relationship with God. And everyone lovingly serving the Supreme Being is in the spiritual realm whether they are in the physical or spiritual realms.

This is why each of us goes through life feeling like something is missing. This is why many try to achieve heaven on earth. This is why each of us feels empty inside, and we try to fill that emptiness with more emptiness - the temporary things and people of the physical world.

The only way back home is to renew our relationship with the Supreme Being. We must re-establish that original relationship. Therefore, we need to be re-introduced to God and be shown how to love Him and serve Him. This was Jesus' role: He came to testify for God. He came to "testify" - to introduce his followers to the Supreme Being.