One With God
God has to exist whether one believes in any God or not. If someone does not believe there is a God, then they will have to be their own God.
The mind directs the body and grows old with the body. But if there is no spirit born in the body then without any spirit there is only an eternally uncomfortable sense of life stuck in a body without fruit. Knowledge of existence is not a spirit of existence.
Being Like Jesus
Everyone already believes God is a Spirit. Believers distinguish God as the Holy Spirit. Since we were created, and that not by ourselves, we take on the personages of the creator. Jesus explains this in John 17. Elsewhere Jesus asks, do we not call ourselves all Gods? Baptist friends call it "little Gods" since they do not see Jesus' view the same way. Jesus, it is remembered, said we would do greater things than He. Those, that is, those of "great faith."