From the Second Vatican Council's Constitution on the Sacred Liturgy (par. 7-8):
To accomplish [the work of our salvation], Christ is always present in His Church, especially in her liturgical celebrations. He is present in the sacrifice of the Mass, not only in the person of His minister, "the same now offering, through the ministry of priests, who formerly offered himself on the cross," but especially under the Eucharistic species. By His power He is present in the sacraments, so that when a man baptizes it is really Christ Himself who baptizes. He is present in His word, since it is He Himself who speaks when the holy scriptures are read in the Church. He is present, lastly, when the Church prays and sings, for He promised: "Where two or three are gathered together in my name, there am I in the midst of them" (Matt. 18:20) .
Christ indeed always associates the Church with Himself in this great work wherein God is perfectly glorified and men are sanctified. The Church is His beloved Bride who calls to her Lord, and through Him offers worship to the Eternal Father.
Rightly, then, the liturgy is considered as an exercise of the priestly office of Jesus Christ. In the liturgy the sanctification of the man is signified by signs perceptible to the senses, and is effected in a way which corresponds with each of these signs; in the liturgy the whole public worship is performed by the Mystical Body of Jesus Christ, that is, by the Head and His members.
From this it follows that every liturgical celebration, because it is an action of Christ the priest and of His Body which is the Church, is a sacred action surpassing all others; no other action of the Church can equal its efficacy by the same title and to the same degree.
In the earthly liturgy we take part in a foretaste of that heavenly liturgy which is celebrated in the holy city of Jerusalem toward which we journey as pilgrims, where Christ is sitting at the right hand of God, a minister of the holies and of the true tabernacle; we sing a hymn to the Lord's glory with all the warriors of the heavenly army; venerating the memory of the saints, we hope for some part and fellowship with them; we eagerly await the Saviour, Our Lord Jesus Christ, until He, our life, shall appear and we too will appear with Him in glory.