Day 152: Lex Orandi, Lex Credendi

"The purpose of the sacraments is to sanctify men, to build up the Body of Christ, and, finally, to give worship to God. Because they are signs, they also instruct. They not only presuppose faith, but by words and objects, they also nourish, strengthen, and express it. That is why they are called 'sacraments of faith."' CCC 1123

Today's reading is another short one in the Catechism, again only five short paragraphs. For the liturgy in the Church, the axiom of lex orandi, lex credendi (the law of praying, the law of believing) applies. Essentially, the teaching and belief of the Church (lex credendi) is made manifest in her liturgy and prayer (lex orandi). See the 2009 educational resource Lex Orandi, Lex Credendi from the USCCB for more. The Catechism Compendium summarizes today's reading as follows:

The sacraments not only presuppose faith but with words and ritual elements they nourish, strengthen, and express it. By celebrating the sacraments, the Church professes the faith that comes from the apostles. This explains the origin of the ancient saying, “lex orandi, lex credendi,” that is, the Church believes as she prays. (#228)

If the sacraments are not mere "ordinances" or empty rituals, as some believe, and they aren't given that they were instituted by our Lord Jesus Christ, it follows that the liturgy of the Church is of considerable significance to us - most especially for the Eucharist. The Catechism Companion, Vol II notes:

They [the sacraments] exist to make us holy; through them, the Church is strengthened and God is worshipped. This is what the sacraments are for and what they do... In the Great Commission, Jesus connects the call to evangelize with the call to baptize. Evangelizing involves offering the sacraments. At every Mass, God is glorified for the good of all the Church... Whether we feel it or not, any time we use the gifts of our Father, he is glorified.  (p. 68) 

The importance of the liturgy is so great, that the Catechism itself notes that it may not be  "modified or manipulated at the will of the minister or the community." Even the Pope "may not change the liturgy arbitrarily" (CCC 1125).

2002 edition of the Missale Romanum

In the Church's liturgy, especially in the sacramental mysteries, the Church acknowledges the apostolic faith and calls us to embrace it with love (CCC 1124). (p. 69)