Any Van Morrison fans on here? What's this one about?

Custardpi

I first heard the somewhat (not on any of his regular studio albums) obscure track "Joe Harper Saturday Morning" a few years ago on a cheap compilation of Van's music. I absolutely love the way it sounds, some great emotion in his vocals on it but am stumped as to the meaning of the song. Anyone know what it's about or what inspired it?

https://www.youtube.com/watch?v=77tBQEDEnV8

When ya thought I was a stranger
When you looked upon me
When I came back
But to take you from disaster
I cannot master the four winds in your shack

In the roamin', in the gloamin'
You have brought and set before me
And I think that it's an omen
I'm just not what so many people see

And you shined your glory all around
Do not disguise what we did
I asked you for half a pound and you said
'Go see Joe Harper, Saturday morning kid'
'Go see Joe Harper, Saturday morning kid'

And the child held a ball
In the garden with the old queen
When ya kissed the lips and heart
Another stranger, ya know what I mean

And ya walked on the streets so lonely
In your own childish way
And ya thought that you would only, ha
Do it for today

And ya shined your glory all around
Do not disguise what we did
I asked you for half a pound and you said
'Go see Joe Harper, Saturday morning kid'
'Go see Joe Harper, Saturday morning kid'

And just stood outside the club
And the rain came down on his head
And it he got all soakin' wet
He says 'Go for yourself'
I said, 'I know'
Show Joe, I ain't conquered yet

And I walk away from the backstreet in the rain
And I saw how many times have I died
Then we turned on outside of the bus shelter
And I jumped on and said, 'Goodbye'

And I shined my glory all around
Did not disguise what I did
Tried to keep it underground but they said
'Go see Joe Harper, Saturday morning, kid'
FADES-
You gotta
Go see Joe Harper, Saturday morning
Saturday morning
Saturday morning