Symmetry is an important principle of harmony, both in the universe and in art. I think Leonard uses it in this verse to imply, ‘a transistion so delicate it cannot be marked’, a coming back to God.I stopped to listen, but he did not come. I began again with a sense of loss. As this sense deepened I heard him again. I stopped stopping and I stopped starting, and I allowed myself to be crushed by ignorance. This was a strategy, and didn't work at all. Much time, years were wasted in such a minor mode. I bargain now. I offer buttons for his love. I beg for mercy. Slowly he yields. Haltingly he moves toward his throne. Reluctantly the angels grant to one another permission to sing. In a transition so delicate it cannot be marked, the court is established on beams of golden symmetry, and once again I am a singer in the lower choirs, born fifty years ago to raise my voice this high, and no higher.
I know of 'golden symmetry' as a term used in the poetry of the middle ages, particularly Latin poetry. I remember a verb in the middle of the line and balancing adjectives on either side, but I might be wrong. Leonard’s use of the word ‘court’ seems to point to that meaning.
To me the lines conjure an image of divine balance and order, with Leonard in his rightful place as ‘a singer in the lower choirs’(ie. human).