The poem's frequent anaphora helps to create the speaker's urgent, insistent tone. The speaker shows flashes of gruff humor, but ultimately, they want to deliver a pointed message: Don't condescend to your elders. Treat them as human beings.
For instance, every single stanza here begins with the word "When"—a word that introduces a description of something the elderly speaker does, like "sitting quietly" or "stumbling." And a line that begins with "Don't" always follows hot on those descriptions' heels! This repeated structure highlights a key fact about the poem: it primarily explains how not to treat seniors. Just because they look lonely or weak from the outside doesn't mean they need condescending "pity" from younger people.
Anaphora also adds special emphasis to the speaker's cry:
Hold! Stop! Don’t pity me!
Hold! Stop your sympathy!
These forceful repetitions don't just make the speaker's feelings clear: they characterize the speaker, making them sound proud, independent, and no-nonsense.
But this speaker has a sense of humor, too. At the end of the poem, anaphora combines with diacope to shape a self-deprecating joke:
A little less hair, a little less chin,
A lot less lungs and much less wind.
Here, the movement from the anaphora of "a little less" into "a lot less" and "much less" makes the speaker sound like they're making a joke at their own expense. They have to admit, they're not as young as they used to be—but their sense of humor is just one part of what still makes them feel "lucky" to be alive.