"The Layers" is rolling in change. Turning, or an object that turns, is important imagery, showcasing the transformation taking place in the poem, though it only occurs twice directly. Kunitz uses language that suggests a cyclical nature to life, without endings, only new beginnings. This idea is perfectly mirrored by the act of turning. See how it goes down in the following passages.
Line 16: Here, angels picking through the debris of the speaker's past "wheel on heavy wings." The word, "wheel," is being used creatively as a verb and as a symbol for both motion and change taking place. The scavenger angel's actions will play an essential role in the speaker's transformation to come.
Line 26: The speaker says, "Yet I turn, I turn," a repetition of words expressing a shift in his internal state from despair to joy. Once he stops focusing on the fleeting things in life and starts concentrating on his core "principle"—he has renewed conviction to press on. This idea continues through line 29 with the speaker's "will intact" and another repetition of "go" occurring at the end of lines 28 and 29. These lines enact a clear shift in direction and show change, or transformation, in the form of forward motion.