"God is a concept"

My accomplished poet and novelist friend Michael H. told me that he loved the Nemerov quote:

...a real killer. A couple of others came to mind when I started thinking about it. One of which is E. A. Robinson (fine poet), who described the world as a giant kindergarten where millions of people were trying to spell "G-O-D" with the wrong blocks. The other quote that came to mind was from John Lennon, in his song "God":

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

I wonder what Lennon meant by that. Does the rest of the song throw any light on it?

I don't believe in magic,
I don't believe in I-ching,
I don't believe in bible...
I just believe in me,
Yoko and me...

Could it be that the pain in question was his own pain? If so, perhaps his not believing (his inability to believe?) was the source of it. For my friend Maliha, "God" is crucially "tied to purpose and meaning." "God" supplies a narrative by which to answer the big question, Why are we here? or What is the purpose of our existence? Maybe it was the same for Lennon, and he was in pain over not being able to find in "God" a reason or purpose for his life.

Michael continued:

Lastly, given our universal ineptitude when it comes to defining that which is clearly undefinable (since it transcends, by definition, all of our attempts to describe it), I always like to remember something Joseph Campbell was quick to reiterate in this regard—he who thinks he knows, doesn't know; he who knows that he doesn't know, knows.

And that reminds me of Robert Frost's little poem, "The Secret Sits":

We dance round in a ring and suppose,
But the Secret sits in the middle and knows.
            [From A Witness Tree, 1942]

Something may know, but we don't.