The raylike accompaniment emanated from a long-necked harp called the kora, plucked by a brawny monk in the choir’s front row. Comprising twenty-one strings that arch, like the cables of a suspension bridge, over a halved and hollowed calabash, it is the emblematic instrument of Mandinka jelis, or griots, a hereditary caste of singer-storytellers renowned as keepers of collective memory. Since the mid-twentieth century, scions of the great jeli families have guided the kora’s emergence onto the global stage, from the stately duets of the Malian virtuosos Ballaké Sissoko and Toumani Diabaté to the late Guinean singer Mory Kanté’s dance hit “Yeke Yeke.” Nevertheless, a pivotal step in its rise occurred at Keur Moussa, whose founders’ quest to Africanize their liturgy revolutionized the instrument. If the kora is now a fixture of world music, lauded by the London Symphony Orchestra and inspiring Donald Glover, it’s partly because of the monks who took it to church.