Just after dawn in Lhamo, a small town on the northeastern corner of the Tibetan Plateau, horns summon the monks of Serti Monastery to prayer. Juniper incense smolders in the temple’s courtyard as monks begin arriving in huddled groups. Some walk the kora, a clockwise circumambulation around the building. Others hustle toward the main door, which sits just inside a porch decorated in bright thangka paintings. A pile of fur boots accumulates outside. When the last monks have arrived, the horn blowers leaning out of the second-floor windows retire indoors.

When I visited Lhamo in 2015, most monks at…