The celebration of the Sacred Liturgy is at the very heart of Catholicism. In fact, Vatican II teaches that "the liturgy is the summit toward which the activity of the Church is directed; at the same time, it is the font from which all her power flows" (Sacrosanctum Concilium, art. 10). In other words, all of the activity of the Christian life is in some way connected to the liturgy, and at the same time all of the grace and power to live out the Christian life flows to us from the liturgy.
Read and Study: United States Catholic Catechism for Adults Chapter 14 (pgs. 165-179)