The falling leaves make the idea of “dropping away” easy to visualize. In تَتَهَافَتُ عَنْهُ ذُنُوبُهُ, عَنْهُ means “from him,” and ذُنُوبُهُ means “his sins.” The word كَمَا means “just as” and connects the two scenes in a comparison.
The comparison does not make sins physical leaves. It uses a familiar pattern—leaves falling away—to convey the spiritual benefit of sincere prayer. The reader should identify the intended point of resemblance rather than impose an unrelated literal meaning.