By Joshua Heavin In the late fourth and early fifth centuries, the church had no shortage of theological controversies and societal crises at hand. Yet several prominent theologians nonetheless devoted significant time to writing about marriage and human sexuality. St. Gregory of Nyssa, for instance, amidst fierce debates over the Trinity, Christology, and the Spirit, while vigorously denouncing the injustices of slavery in a declining empire, devoted fifteen beautiful homilies to theological and mystical reflections on the Song of Songs.…