God is a concept, by which we measure our pain.

What did John Lennon mean by singing this in this song?
quote from the song :

I don’t believe in magic
I don’t believe in I-ching
I don’t believe in bible,
I don’t believe in tarot,
I don’t believe in Hitler,
I don’t believe in Jesus,
I don’t believe in Kennedy,
I don’t believe in Buddha,
I don’t believe in mantra,
I don’t believe in Gita,
I don’t believe in yoga,
I don’t believe in kings,
I don’t believe in Elvis,
I don’t believe in Zimmerman,
I don’t believe in Beatles,
I just believe in me,
Yoko and me,
And that’s reality.