In his masterwork, Die geestelijke brulocht (The Spiritual Espousals), the fourteenth-century Flemish mystic Jan van Ruusbroec used his profound knowledge of Trinitarian theology to show that the apex of the spiritual life consists in our being taken up into the love of the three persons of the blessed Trinity. The care and precision with which Ruusbroec describes the ascent from "the active life" to "the interior life" and from there to the...