Our Catholic Mass includes Word and Sacrament. We hear God’s Word spoken to us through the scriptures and in the homily. We respond to that Word with our prayers and in receiving the body and blood of Our Lord, Jesus Christ. All of our hope is placed in the saving power of God’s word and presence, most especially in His presence that comes to us in the Eucharist.
As the heart of the Catholic Church, the Mass conveys the depth of Catholic theology, especially in the Eucharist, which is at its center. Rich in symbolism, the Mass provides a deeply sacred moment for those who participate in it, and even sometimes for those who observe it. For Catholics, receiving the Holy Eucharist completes the rite of Christian initiation. Those who have been raised to the dignity of the royal priesthood by Baptism and configured more deeply to Christ by Confirmation participate with the whole community in the Lord’s own sacrifice by means of the Eucharist.
“At the Last Supper, on the night he was betrayed, our Savior instituted the Eucharistic sacrifice to his Body and Blood. This he did in order to perpetuate the sacrifice of the cross throughout the ages until he should come again, and so to entrust to his beloved Spouse, the Church, a memorial of his heath and resurrection: a sacrament of love, a sign of unity, a bond of charity, a Paschal banquet ‘in which Christ is consumed, the mind is filled with grace, and a pledge of future glory is given to us."
(The Catechism of the Catholic Church 1322 & 23 – for more information see 1324 – 1421)
So rich is the mystery of the Eucharist that we have a number of terms to illumine its saving grace: the Breaking of the Bread; the Lord's Supper; the Eucharistic Assembly; the Memorial of Christ's Passion, Death, and Resurrection; the Holy Sacrifice of the Mass, the Holy and Divine Liturgy; the Eucharistic Liturgy; Holy Communion; and Holy Mass (cf. CCC, nos. 1328-1332).
We understand prayer through our celebration of the Sacraments and in the Liturgy of the Hours. The word liturgy comes from a Greek term meaning "public work or work done on behalf of the people." A work, then, done by an individual or a group was a liturgy on behalf of the larger community. All the worshipers are expected to participate actively in each liturgy, for this is holy "work," not entertainment or a spectator event. Every liturgical celebration is an action of Christ the High Priest and of his Mystical Body, which is the Church. It therefore requires the participation of the People of God in the work of God.
Liturgy is centered on the Holy Trinity. At every liturgy the action of worship is directed to the Father, from whom all blessings come, through the Son in the unity of the Holy Spirit. We praise the Father who first called us to be his people by sending us his Son as our Redeemer and giving us the Holy Spirit so that we can continue to gather, to remember what God has done for us, and to share in the blessings of salvation.
From the United States Catholic Catechism for Adults
Source: United States Conference of Catholic Bishops