"It [the sacred liturgy] is therefore the privileged place for catechizing the people of God." CCC
But what does this have to do with the liturgy? Our approach to the liturgy shares in these two aspects: the sensory/experiential and the intellectual. Sometimes there are those who focus upon the intellectual teaching of the Faith who question the importance of the liturgy in its outer aspects; they would suggest that what matters is not so much how we do something, but rather that we simply know (intellectually) what we are doing. In regards the sacred liturgy, they often think that it does not matter so much how the liturgy is celebrated so long as one knows what the liturgy is all about in general. But, this thinking is not in accord with the mind of the Church and fails to understand how the actions of the liturgy connect to doctrine and pass on the Faith; it also fails to recognize the importance of the experiential aspect of human learning. Two comments that often reveal a lack of understanding of the liturgy-doctrine connection are these: "all that matters in the Mass is that Our Lord is present in the Eucharist" or "to be concerned about vestments, music, and other externals in the Mass is pharisaical."
Now, we should be clear from the outset that the didactic aspect of the liturgy is not its primary aspect; rather, the worship of God is the primary aspect. But this said, the Church teaches us that the liturgy, by its nature, does have a didactic dimension. This didactic, or catechetical dimension comes to us not only through the intellect (e.g. studying our catechism and homilies) but it also comes to us through our experience of it; that is, through our senses.
Lex orandi; lex credendi (The law of prayer is the law of belief.)
I spoke earlier of our human nature and how we learn, and who would know this nature better than God, our Creator? It makes perfect sense, then, that God would provide and inspire, through the authority of the Church, all that is necessary for the faithful to learn about Him, to worship Him and ultimately draw closer to Him through the liturgy by way of its words, beauty, ceremonies, gestures, postures, signs, symbols, sacred art, and sacred music. All of these visible things help to draw us from the visible to the invisible; they draw us toward the transcendent that we may be able to more deeply unite ourselves to the sacred mysteries taking place in our midst. Of course, this is not to deny the place of intellectual catechesis as well. It is also through mystagogical catechesis -- the intellectual explanation of the sacred mysteries, gestures, etc, within the liturgy -- by way of the homily, personal study, catechism classes, and so forth, that the faithful are able to know what the visible realities represent in terms of spiritual realities.
"For the Sacred Liturgy is quite intimately connected with principles of doctrine.."(RS)
The Holy Father has been drawing our attention, through his words and deeds, to the understanding that everything matters in the sacred liturgy. He has written and spoken of the need to see the liturgy as a whole that cannot be taken apart, added to or subtracted from, without affecting all of the other parts. This is because everything in the liturgy, words and gestures, is intertwined with Catholic doctrine; the Church safeguards this through the authorized texts, rubrics, and instructions. It is for this reason, therefore, that introducing aspects into the liturgy which are not authorized is prohibited. It is for this reason that the liturgy cannot and should not be arbitrarily changed; abuses in the liturgy obscure Catholic doctrine and subsequently the errors are passed on to the faithful. It is also for this reason that everything (licitly) done within the liturgy, and in continuity with liturgical tradition, can serve as a light to brighten and make clearer the doctrines of the Church and the sacred mysteries being encountered. As the Holy Father has stated and witnesses to us, the external forms of the liturgy are not inconsequent or mere pharisaism rather they are of great importance for the experiential in teaching and passing on the Faith.
"The entire liturgy, therefore, has the Catholic faith for its content.." (Pope Pius XII)
The sacred liturgy is an essential means for the transmission of the Faith. The Catholic faith cannot be passed on and learned through the intellect alone; it must be understood that an experiential aspect is necessary to fully teach the Faith and make it incarnate in each of the faithful. The catechical nature of the sacred liturgy is an important aspect to realize since the majority of the faithful do not study the catechism or theology on their own and often the weekly liturgy may be the only contact they have with their Catholic faith. It is through the authorized liturgical rites celebrated with a sense of mystery, beauty, and reverence, evidenced in every word, gesture, and every piece of sacred art, that the truths of the Catholic faith will be learned, experienced and passed on.
I would like to simply share a few relevant quotes that may be helpful in driving some of these points home. Perhaps they might be useful to priests for catechetical purposes as well:
"The liturgy is the summit toward which the activity of the Church is directed; it is also the font from which all her power flows." It is therefore the privileged place for catechizing the people of God. "Catechesis is intrinsically linked with the whole of liturgical and sacramental activity, for it is in the sacraments, especially in the Eucharist [the liturgy], that Christ Jesus works in fullness for the transformation of men." (Catechism of the Catholic Church #1074)
"[I]t must first be said that "the best catechesis on the Eucharist [the liturgy] is the Eucharist itself, celebrated well." By its nature, the liturgy can be pedagogically effective in helping the faithful to enter more deeply into the mystery being celebrated. That is why, in the Church's most ancient tradition, the process of Christian formation always had an experiential character. While not neglecting a systematic understanding of the content of the faith, it centred on a vital and convincing encounter with Christ, as proclaimed by authentic witnesses." (Pope Benedict XVI, Sacramentum Caritatis #64)
"The liturgy is the first source of the divine communion in which God shares his own life with us. It is also the first school of the spiritual life." (Pope Paul VI)
"There is thus a close connection between dogma and the sacred Liturgy, and between Christian worship and the sanctification of the faithful." (Pope Pius XI, Divini Cultus)
"The sacred liturgy.. is the primary and indispensable source from which the faithful are to derive the true Christian spirit." (Sacrosanctum Concilium #14)
"For the Sacred Liturgy is quite intimately connected with principles of doctrine, so that the use of unapproved texts and rites necessarily leads either to the attenuation or to the disappearance of that necessary link between the lex orandi and the lex credendi." (Redemptionis Sacramentum #10)
"The liturgical words and rites, moreover, are a faithful expression, matured over the centuries, of the understanding of Christ, and they teach us to think as he himself does; by conforming our minds to these words, we raise our hearts to the Lord. All that is said in this Instruction is directed toward such a conformity of our own understanding with that of Christ, as expressed in the words and the rites of the Liturgy." (Redemptionis Sacramentum #5)
"For abuses “contribute to the obscuring of the Catholic faith and doctrine concerning this wonderful sacrament”. (Redemptionis Sacramentum #6)
"We observe with considerable anxiety and some misgiving, that elsewhere certain enthusiasts, over-eager in their search for novelty, are straying beyond the path of sound doctrine and prudence. Not seldom, in fact, they interlard their plans and hopes for a revival of the sacred liturgy with principles which compromise this holiest of causes in theory or practice, and sometimes even taint it with errors touching Catholic faith and ascetical doctrine." (Pope Pius XII - Mediator Dei #8)
"[A]s Catholic doctrine on the Incarnate Word of God, the eucharistic sacrament and sacrifice, and Mary the Virgin Mother of God came to be determined with greater certitude and clarity, new ritual forms were introduced through which the acts of the liturgy proceeded to reproduce this brighter light issuing from the decrees of the teaching authority of the Church, and to reflect it, in a sense so that it might reach the minds and hearts of Christ's people more readily." (Pope Pius XII - Mediator Dei # 52)
"The entire liturgy, therefore, has the Catholic faith for its content, inasmuch as it bears public witness to the faith of the Church." (Pope Pius XII - Mediator Dei #47)