At four in the morning, the speaker wakes or sits up in the dark and notices that their ears are "coming clear." It's the moment when the usual background hum of the world has dropped away, and small sounds start to come through sharply. The poem's surprise is its last line, where that sensation is compared to "the lives of nuns."
That comparison does a lot in very few words. Nuns are associated with quiet, discipline and a life set apart from noise, so the image suggests a hearing that is clean, uncluttered and almost devout. The speaker doesn't say they feel peaceful or lonely, but the tone points toward calm, attentive stillness, maybe with a slight sense of being apart from everyone else who is asleep. The odd pairing of something physical, ears clearing, with something spiritual makes listening feel like a quiet kind of practice. The title, "Silence," ties it together: silence here isn't empty, it's what lets you finally hear.