The Second Vatican Council 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." The Eucharist and the celebration of the sacrifice of the Mass is at the very heart and center of the Christian life. It stands as the pinnacle of the New Covenant established by Christ, and the Eucharist is the source of the unity of the Church.
Read and Study: United States Catholic Catechism for Adults Chapter 17 (pgs. 213-232)