From the Catechism of the Catholic Church, Simplified
Retaining Old Testament Images (1093-1095)
Because the Spirit fulfills the Old Covenant, the liturgy retains certain Old Covenant elements (such as readings from the Old Testament, the praying of the Psalms and the recalling of the saving events, especially the Exodus and the Passover).
The Church's catechesis reveals the mystery of Christ which is hidden in Old Testament images. The flood, Noah's ark, the cloud, and the crossing of the Red Sea symbolize Baptism. The water from the Rock prefigures the spiritual gifts of Christ, and the manna prefigures the Eucharist, "the true bread from heaven" (Jn 6:32).
The Church re-reads and relives salvation history in the "today" of her liturgy. Catechesis must lead to a spiritual understanding of this economy of salvation revealed in the liturgy.
Jewish Source but Christian Faith (1096)
Knowing the Jewish people's faith helps us to understand the Christian liturgy. The structure of the Liturgy of the Word originates in Jewish prayer. The Eucharistic Prayers draw inspiration from the Jewish tradition. However, the differences between the two are important. Christians and Jews both celebrate the Passover, but the Jews see it as history, while Christians see the Passover as being fulfilled by Jesus' death and Resurrection (while still expecting its divine fulfillment).
Preconditions for the Encounter (1097-1098)
Every New Covenant liturgical action is an encounter between Christ and his Church. The Spirit gathers people of every race and social background in a unified assembly, "a communion of the Spirit."
To prepare itself, the assembly must allow the Spirit to awaken faith, conversion, and adherence to the Father's will. These are the preconditions for producing fruits of a new life.
The Spirit and God's Word (1099-1102)
The Spirit (the Church's living memory) and the Church itself manifest Christ and his work in the liturgy.
The Spirit gives life to the proclaimed Word of God. Scripture is extremely important in the liturgy. It provides the readings, inspires the hymns and prayers, and gives meaning to the actions.
The Spirit gives a spiritual understanding of God's Word to the people and ministers, placing in them a relationship with Christ so they can live out what they celebrate.
The Spirit gives the grace of faith so that the saving Word of God elicits a response of faith and the assembly "a communion in faith."
Making a Remembrance (1103)
In the Liturgy of the Word, the Spirit "recalls" all that Christ had done. The celebration "makes a remembrance of all God's works." By this remembering ("anamnesis") the Spirit awakens the memory of the Church which then gives thanks.
Making the Mystery Present (1104-1105)
Besides recalling, the Christian liturgy also actualizes the saving events. Christ's Paschal mystery is celebrated (not repeated). In these celebrations the Holy Spirit makes the mystery present.
At the invocation (epiclesis) the priest asks the Father to send the Spirit upon the bread and wine so that they become the body and blood of Christ.
Spirit's Transforming Power (1106-1107)
This remembering (anamnesis) and this begging the Father to send the Spirit (epiclesis) is at the heart of the sacramental celebration. St. John Damascene explains how the bread and wine become the body and blood of Christ: "Let it be enough for you to understand that it is by the Holy Spirit, just as it was of the Holy Virgin and by the Holy Spirit that the Lord took flesh."
The Holy Spirit's transforming power hastens the coming of the kingdom, causing us to anticipate our full communion with the Trinity.
Fruits of the Liturgy (1108-1109)
In every liturgical action, the Holy Spirit (the sap of the Father's vine) brings about fruit. He abides indefectibly in the Church and makes the Church the great sacrament of divine communion. Communion with the Trinity and other believers are the fruit of the Spirit in the liturgy.
This "fellowship of the Holy Spirit" (2 Cor 13:13) transforms the faithful and helps them to participate in the Church's mission.