The literary/poetic device that opens "Wild Geese" is a figure of speech word scheme called anaphora. This is the repetition of a word group at the beginning of successive sentences. Specifically, Oliver opens with "You do not..." and repeats the word group in the next sentence/poetic line, "You do not...." In addition, Oliver adds a modified anaphora with the repetition of "You ..." in the forth line.
The second instance of anaphora is in the repetition of "Meanwhile the ...." Repetition draws attention to the point being made and adds potency (i.e., power) to the concept. Note that in each instance of anaphora one or more lines interrupt the second and third repetitions:
You do not have to be good.
You do not have to walk on your knees
for a hundred miles through the desert repenting.
You only have to let the soft animal of your body
Meanwhile the world goes on.
Meanwhile the sun and the clear pebbles of the rain
are moving across the landscapes,
over the prairies and the deep trees,
the mountains and the rivers.
Meanwhile the wild geese, high in the clean blue air,
Another poetic device (when literary devices are employed in the composition of poetry, they are correctly referred to as poetic devices) Oliver uses is metaphor. Two instances of metaphor are:
the soft animal of your body
the clear pebbles of the rain
Metaphor is the comparison between two unlike things to shed light upon the nature or quality of one of the pair either because it is less familiar or because the poet wants to present a new dimension or a new way of looking at something that is familiar.
In the first metaphor above, Oliver is presenting a new way of thinking of one's very familiar body; she conjures the image of one's body as a soft furry animal, like a bunny or kitty or puppy, in order to give a new and more sympathetic way of looking at one's body.
In the next, "clear pebbles of the rain," she gives a new dimension to very familiar rain. Care has to betaken here, though, as pebbles might be associated with harm (e.g., rocks thrown), whereas, in fact, the meaning of the metaphor must be associated with the movement of the rain ("over prairies and deep trees") and with the role of the "world"--of which rain is a part--in the last lines of the poem: "the world ... / calls to you ... / ... / in the family of things." The rain, "clear pebbles," is a gentle, though forceful member of the "world," which adds a potency to the world that calls.
A third poetic device is the personification of "world" through a pathetic fallacy. The personified world, by use of pathetic fallacy (i.e., inanimate nature given human characteristics and qualities), "offers" to you, "calls to you," and announces to you "your place / in the family of things" ... "no matter how lonely" you are. Oliver's objective in using each of these poetic devices is to lend potency to a friendly world and to one's view of one's self.