The speaker, a farmer, begins with a strange comparison: raising a rose is like giving salt to a fish. A fish already lives in salt water, so the gift is pointless. The image suggests that making something beautiful and decorative feels unnecessary, even a little absurd, to someone who works the land. The speaker admits plainly, "I had no great pleasure in it."
The second stanza turns. The word "but" shifts the feeling from indifference to quiet appreciation. What the speaker does value is the fields, bare and "all in dirt." Calling them "livable prayers" is the poem's richest moment. A prayer is usually words or a wish, but here it is something you can actually live inside and work within. The poem seems to say that real devotion lies in ordinary, useful ground rather than in showy flowers.
The mood is spare, humble, and calm. The speaker doesn't boast or preach, and the short lines let the thought settle slowly.