The Liturgy of the Church
In the sacramental liturgy of the Church, the mission of Christ and of the Holy Spirit proclaims, makes present, and communicates the mystery of salvation, which is continued in the heart that prays. The spiritual writers sometimes compare the heart to an altar. Prayer internalizes and assimilates the liturgy during and after its celebration. Even when it is lived out "in secret," prayer is always prayer of the Church; it is a communion with the Holy Trinity.
Source: Catechism of the Catholic Church (Vatican.va)