It would be easy to dismiss this collection, a Pulitzer Prize winner, as just another nature collection, but that would, I think, be to miss the point. Sure enough, there are flowers, but the persona, perhaps Gluck, is angry. Her tone with her listener (God?) is aggressive. Consider –
What is my heart to you
that you must break it over and over
like a plantsman testing
his new species? Practice
on something else.
Note the imperative – practice. And the slightly dismissive tone inherent in that word choice.
Gluck has boundaries on her mind – between time, especially seasons, and between humans and their version of God.
As for why there are 9 poems called “Vespers,” no idea!