Book excerpt: The Catholic Church teaches that the celebration of the liturgy is the “source and summit of the Christian life” (Lumen gentium, 11). Participating in the liturgy—the Mass, the Liturgy of the Hours, the sacramental rites, blessings, and other official rites—is the most important act of Catholic Christians, for it is through the liturgy that the faithful give praise to God, thank him for his blessings, and go forth strengthened and challenged to life as Christ’s disciples in the world. This easy-to-read resource explores what it means to call liturgy “source and summit.” It will help the Catholic faithful to understand the meaning of the liturgy and its importance to our life of faith, experience Christ’s four-fold presence in the various Church rites, come to a deeper relationship with God, and reflect on the transforming power of the liturgy to change the world.