44. Christ’s word gathers the people of God as one and increases and sustains them. “This applies above all to the liturgy of the word in the celebration of Mass, where there are inseparably united the proclamation of the death of the Lord, the response of the people listening, and the very offering through which Christ has confirmed the New Covenant in his Blood, and in which the people share by their intentions and by reception of the sacrament.” [Presbyterorum Ordinis 4] For “not only when things are read ‘that 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 rightful worship and receive his grace more abundantly.” [Sacrosanctum Concilium 33]
It’s accurate to suggest that the Liturgy of the Word has a twofold purpose: evangelization and spiritual sustenance. The context of that first Vatican II quote is the notion that the proclamation of the Word is the priest’s first duty. From the view of the laity, one of our first duties as a Christian is to listen and to respond. Hence the mention again of the twofold role of the laity at Mass: to worship God and to be open to the reception of divine grace. The next four numbered sections expand on this a bit–and that’s before we get to specific ministries of deacon, lector, psalmist, and commentator.