In this practical guide to spiritual growth, Fr. José Guadalupe Treviño outlines the divinely ordained laws that govern the interior life and lead the soul toward holiness. Devoting a chapter to each of eighteen foundational rules, he explains how to overcome obstacles to prayer, identify your predominant fault, root out venial sin, and grow in recollection and awareness of God’s presence. Drawing on St. Thomas Aquinas and the wisdom of the tradition, he clarifies the path from beginner to deeper surrender, highlighting the signs of progress and the dangers of lukewarmness or imbalance. This classic work directs readers to the source of all holiness and the faithful love that unites the soul to God.