The poem uses several kinds of repetition. First, it repeats, or nearly repeats, several line-ending words: "mirror" (lines 4 and 14), "heart" (lines 8 and 11), and "come"/"welcome" (lines 1 and 5). Like a very loose rhyme scheme, these pairings add a degree of structure to the poem, while tying in with the poem's theme of divided/paired selves. The doubling of "mirror" is especially appropriate, since mirrors create doubles.
The poem also depends heavily on repetition in the form of parallelism. Roughly half of the poem is structured in parallel clauses, as in line 4:
at your own door, in your own mirror
Later, the repetition of "Give" is more specifically an example of anaphora:
Give wine. Give bread. Give back your heart
More parallelism follows after this as well. Note the repeated structures in the clauses below:
to itself, to the stranger who has loved you
[...] whom you ignored
[...] who knows you by heart
[...] the love letters
[...] the photographs, the desperate notes.
Lines 6 and 15 are yet more examples of parallelism, as each contains double commands with similar phrasing ("sit here. Eat"; "Sit. Feast").
The inclusion of all these repetitive structures makes the poem strongly rhythmic. The rhythm, in turn, sounds soothing—as fits the poem's reassuring message—but also authoritative, as the speaker layers instruction on top of instruction. In other words, the poem's repetitions reinforce not only its themes but also its tone, as the speaker guides the reader through the aftermath of heartbreak.