The poem begins on a note of gentle instruction as the speaker addresses a general "you" in a tone of familiarity, like that of a mentor encouraging a student. Without mentioning a specific god or faith, the speaker explains how to pray. Prayer, here, is not a request for forgiveness or favors but a meditative practice in which "you open your whole self" to the universe.
In paying close attention to that universe, the speaker suggests, you will hear "one whole voice that is you." In other words, by extending your focus beyond the narrow boundaries of your self, you'll discover that your self is deeply connected with everything that surrounds it: with the "sky," "earth," "sun," "moon," and so on. The repetition of "whole" (lines 1 and 3) emphasizes that people's inner and outer worlds—self and universe—are part of the same, inseparable entity:
To pray you open your whole self
[...]
To one whole voice that is you.
The poem is written in free verse, but line 2 ("To sky, to earth, to sun, to moon") features a steady iambic rhythm. Iambic meter is sometimes compared to the ba-bum of a heartbeat. Here, it might evoke the heartbeat of some who's praying, meditatively listening to the rhythms of their body and the surrounding world.
Also notice that the list in lines 2-3 omits a connecting "and," in a device known as asyndeton. Even the comma after "moon" is missing:
To sky, to earth, to sun, to moon
To [...]
These omissions make the items in the list seem all the more closely joined together, reinforcing the speaker's point that everything in the universe is connected.