The Liturgy as a Source of Instruction
Although the sacred liturgy is above all things the worship of the divine Majesty, it likewise contains much instruction for the faithful (Council of Trent, Session XXII, Doctrine on the Holy Sacrifice of the Mass, c. 8). For in the liturgy God speaks to His people and Christ is still proclaiming His gospel. And the people reply to God both by song and prayer.
Moreover, the prayers addressed to God by the priest who presides over the assembly in the person of Christ are said in the name of the entire holy people and of all present. And the visible signs used by the liturgy to signify invisible divine things have been chosen by Christ or the Church. Thus not only when things are read "which were written for our instruction" (Rom. 15:4), but also when the Church prays or sings or acts, the faith of those taking part is nourished and their minds are raised to God, so that they may offer Him their rational service and more abundantly receive His grace.
Constitution on the Sacred Liturgy, Sacrosanctum Concilium # 33.