Each of the spiritual classics in The Wellsprings of Faith—Thomas à Kempis' The Imitation of Christ, Teresa of Avila's The Interior Castle, and St. John of the Cross' The Dark Night of the Soul—remains strikingly fresh and relevant for modern readers. The books continue to inspire believers today, and yet were either products of conflict within the Church or agents of religious upheaval. Thomas à Kempis' The Imitation of Christ touches seekers with its powerfully personal spiritual advice, while Teresa of Avila's The Interior Castle and St. John of the Cross' The Dark Night of the Soul show seekers how to have a personal union with Christ, instead of a relationship solely with the Church.