God is an experience and not a concept.
Once in a small village, a mystic sat under a tree, surrounded by his disciples in deep silence. A well known scholar and logician who was an atheist approached the master. The atheist said to the master that he has come to him with a question to be answered. He then asked, "What is the proof of God?"
The mystic opened his eyes and answered, "If you want the proof of God, look into the eyes of the devotees. There is no other proof"
Osho says, God is a reality. God is an experience and not a concept to be reasoned out logically. God is the subjective experience in the deepest core of the heart. God is the experience of the inner most centre. When one is centered one knows.