I suppose we could always ask Richard but I think he doesn't do explanations unless he's in a really good mood. I believe it was written at Little Hadham during his "astrology/archery/William and the Outlaws" period

One person's interpretation is here:
http://www.shogem.co.uk/chuck/thanks.htm

which is OK but I suspect a bit too literal.

Anyway I want it at my funeral, not just yet though I hope!