The speaker begins by addressing an unidentified "you." Rather than speaking directly to a specific person, it seems likely that the speaker intends to address anyone who reads the poem. The "you," in other words, refers to all of humanity.
That general human audience, according to this speaker, needs to hear this message: "You do not have to be good." These words acknowledge the pressure people often feel to be morally flawless. By urging readers to leave behind the idea that they always have to be "good," the speaker opens the poem in a welcoming, gentle way, inviting people to embrace normal human imperfection.
The speaker goes on:
You do not have to walk on your knees
for a hundred miles through the desert, repenting.
The phrase "you do not have to" is an anaphora, since the speaker uses the exact same words at the beginning of the first line. This repetition adds rhythm to the beginning of the poem while also stressing the idea that people aren't required to act or feel a certain way. While society might make it seem like people must strive for perfection (or else feel guilty and ashamed), "Wild Geese" tries to free readers of such unforgiving expectations.
The speaker is also making a general allusion with these words. This image of people wandering the desert recalls biblical or religious tales—for instance, the wanderings of the Israelites in the Book of Exodus, or the stories of desert mystics who went through agonies and temptations in the wilderness. This dramatic allusion adds a little humor at the reader's expense: probably nothing you've done, the speaker seems to say, is so bad that you need to crawl through the desert on your hands and knees to make up for it.
The gentle, loving message of these first lines is that it's okay to be imperfect. Life, the speaker implies, is hard enough as it is, so there's no need for people to beat themselves up for failing to "be good." This perspective lays the groundwork for the speaker's later, bigger point: people, this poem will say, can find relief from their petty concerns in the grandeur of nature.