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!