The word liturgy is often used by Catholics as synonymous with the Holy Sacrifice of the Mass. While all of liturgy culminates in the Mass, the Mass is not the whole of liturgy. The word liturgy can signify a variety of other services as well.
Liturgy at its root means an obligation or a duty. For Catholics the liturgy is much more than an obligation or a duty. The Church has participated in the Liturgy since her inception but it was not until the 18th century that liturgy received the meaning it has today. The two most important contemporary documents on the liturgy are Vatican II’s Sacrosanctum Concilium, and Pope Pius XII’s encyclical Mediator Dei. Understanding what these two documents teach regarding the liturgy gives a very good insight into what exactly liturgy is. This short summary will briefly explain liturgy through these two great works.
Pope Pius XII’s encyclical Mediator Dei was given on November 20th 1947. At the heart of the encyclical it defines the liturgy by saying, “the liturgy is nothing more or less than the exercise of this priestly function of Christ.” The liturgy is an efficacious sign of a supernatural reality. The liturgy is not efficacious because of the great work of man but because of the presence of Christ and the actions of the Holy Spirit. The Christian people participate in this work under the direction of the ministerial priesthood that was instituted by Christ. Man does not do liturgy, rather he participates in the liturgy through the invitation of Christ and the indwelling of the Holy Spirit under the direction of the ministerial priesthood. Mediator Dei teaches that in the liturgy one participates in the work of Christ.
Mediator Dei highlights the relationship in the liturgy between God and man. In the liturgy there is an upwards trend of man calling out to God called the anabatic and a downward trend of God to man called the katabatic. The katabatic is the reality of God sending down his graces of redemption upon the members of His Church in the liturgy. The anabatic or upward trend is man offering up to God his adoration and petition through the priest who acts as the mediator between God and man.
The Second Vatican Council strove to build on the truths of Mediator Dei to come to a deeper understanding of liturgy. The fruit of this desire is the document Sacrosanctum Concillium, promulgated on December 4th 1963 by Pope Paul VI. The fathers of the Council attempted to avoid a scholarly definition of liturgy and rather relied on the words of the Bible and the Church Fathers. The document defines the liturgy by claiming, “the liturgy is considered as an exercise of the priestly office of Jesus Christ. In the liturgy, by means of signs perceptible to the senses, human sanctification is signified and brought about in ways proper to 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.”
Through this definition, the document declared four essential aspects of liturgy. First, the liturgy is not the work of man but rather is an exercise of Christ’s priestly office. Secondly, the liturgy is performed through the uses of signs that can be embraced through the senses. Thirdly, through these signs human sanctification is not only signified but is also brought about. Lastly, the document teaches that while liturgy is the exercise of Christ’s priestly office it is the work of the whole Mystical Body of Christ: both Christ the Head and all the members. In other words, in the liturgy the people of God participate in the priestly office of Christ according to their state in life.
These two great modern documents on the liturgy Pope Pius XII’s Mediator Dei and Vatican II’s document Sacrosanctum Concilium give a great insight into what the liturgy is. Through a more scholarly presentation in Mediator Dei and a more contemplative presentation in Sacrosanctum Concilium it is clear that the liturgy is not a spectator event. All Christians are invited to full participation in the liturgy, to participate in the priestly office of Christ, whereby God sends down his redemptive grace and He receives our prayers of adoration and petition.
 Pope Pius XII, Encyclical on The Sacred Liturgy Mediator Dei(20 November 1947), §22, at Castel Gandolfo, www.vatican.va.
 Pope Paul VI, Constitution on The Sacred Liturgy Sacrosanctum Concillium (4 December 1963), §7, at The Vatican, http://www.vatican.va.
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