What does the speaker in "my heart leaps up" mean by the phrase "natural piety"?

We suspect that the speaker doesn't mean literal days here, but rather his time on earth—his life. The glue, or rope, between these days is "natural piety." ... We think the speaker wants his days to be tied together by reverence and piety toward the natural world, rather than toward religion.

the correct answer would be d.

we need more information in order to answer.