The speaker looks back at an earlier version of themselves and asks who that person was. The answer the poem circles around is a self ruled by appetite rather than thought. "The city of desire" suggests a place of crowded wants, and the speaker was "too free" there, moving without restraint or much reflection. Nothing had yet filled the head, so the belly did the deciding.
The final image shifts from the city to the countryside: "raw ground in fields," lazy and reckless with sun and sleep. It compares that younger self to untended earth, soaking up warmth and resting without any purpose. "Wanton" carries a hint of both pleasure and waste.
The mood is reflective and a little puzzled, with tenderness mixed in. The speaker doesn't seem to scold their past self so much as marvel at it. The title, "Natural piety," hints that this instinctive, unthinking life might have its own kind of devotion, a trust in the body and the natural world.