You can't really talk about Wallace Stevens without talking about spirituality. Whenever the speaker of "Of Modern Poetry" says that modern poetry has to find something that's good enough ("will suffice") for modern people, he means good enough in a really deep way—as in good enough to make life seem like it's worth living, good enough to make you think the world might actually care about you. The world doesn't always make us feel that way, especially the modern world. So for Stevens, it's up to poetry to fill the void and make us feel spiritually better about our lives.
Hallelujah! For Stevens, poetry is the new religion. People can't live without a sense of meaning in the universe, and there's no way science can give it to them.
Thanks bunches, Wallace. "Of Modern Poetry" gives us an exact blueprint for how we can start to find deeper spiritual meaning in our lives.