11.] The Mystery of the Eucharist "is too great for anyone to permit himself to treat it according to his own whim, so that its sacredness and its universal ordering would be obscured".  On the contrary, anyone who acts thus by giving free reign to his own inclinations, even if he is a Priest, injures the substantial unity of the Roman Rite, which ought to be vigorously preserved, and becomes responsible for actions that are in no way consistent with the hunger and thirst for the living God that is experienced by the people today. Nor do such actions serve authentic pastoral care or proper liturgical renewal; instead, they deprive Christ’s faithful of their patrimony and their heritage. For arbitrary actions are not conducive to true renewal, but are detrimental to the right of Christ’s faithful to a liturgical celebration that is an expression of the Church’s life in accordance with her tradition and discipline. In the end, they introduce elements of distortion and disharmony into the very celebration of the Eucharist, which is oriented in its own lofty way and by its very nature to signifying and wondrously bringing about the communion of divine life and the unity of the People of God. The result is uncertainty in matters of doctrine, perplexity and scandal on the part of the People of God, and, almost as a necessary consequence, vigorous opposition, all of which greatly confuse and sadden many of Christ’s faithful in this age of ours when Christian life is often particularly difficult on account of the inroads of "secularization" as well.
[12.] On the contrary, it is the right of all of Christ’s faithful that the Liturgy, and in particular the celebration of Holy Mass, should truly be as the Church wishes, according to her stipulations as prescribed in the liturgical books and in the other laws and norms. Likewise, the Catholic people have the right that the Sacrifice of the Holy Mass should be celebrated for them in an integral manner, according to the entire doctrine of the Church’s Magisterium. Finally, it is the Catholic community’s right that the celebration of the Most Holy Eucharist should be carried out for it in such a manner that it truly stands out as a sacrament of unity, to the exclusion of all blemishes and actions that might engender divisions and factions in the Church.
The preceding is an excerpt from the Preamble to Redemptionis Sacramentum, paragraphs 11-12.
This document originates from Pope John Paul II's encyclical letter, Ecclesia de Eucharistia. John Paul II states that the eucharist is the "most precious possession"  the Church has and there fore the "liturgical norms for the celebration of the Eucharist be observed with great fidelity" (no. 52). John Paul II in his letter asked that the offices of the Roman Curia "prepare a more specific document, including prescriptions of a juridical nature, on this very important subject. No one is permitted to undervalue the mystery entrusted to our hands: it is too great for anyone to feel fee to treat it lightly and with disregard for its sacredness and its universality" (no. 52). 
Pope John Paul II, Encyclical Letter Ecclesia de Eucharistia, n. 52: AAS 95 (2003), p. 468.
 Second Vatican Ecumenical Council, Constitution on the Sacred Liturgy, Sacrosanctum Concilium, nn. 4,38; Decree on the Catholic Eastern Churches, Orientalium Ecclesiarum, 21 November 1964, nn. 1,2,6; Pope Paul VI, Apostolic Constitution Missale Romanum: AAS 61 (1969) pp. 217-222; Missale Romanum, Institutio Generalis, n. 399; Congregation for Divine Worship and the Discipline of the Sacraments, Instruction Liturgiam authenticam, 28 March 2001, n. 4: AAS 93 (2001) pp. 685-726, here p. 686.
 Cf. Pope John Paul II, Apostolic Exhortation Ecclesia in Europa, n. 72: AAS 95 (2003) p. 000.
 Cf. Pope John Paul II, Encyclical Letter Ecclesia de Eucharistia, n. 23: AAS 95 (2003) pp. 448-449; S. Congregation of Rites, Instruction Eucharisticum mysterium, 25 May 1967, n. 6: AAS 59 (1967) p. 545.
 S. Congregation for the Sacraments and Divine Worship, Instruction Inaestimabile donum: AAS 72 (1980) pp. 332-333.
 Cf. 1 Cor 11,17-34; Pope John Paul II, Encyclical Letter, Ecclesia de Eucharistia, n. 52: AAS 95 (2003) pp. 467-468
 Redemptionis Sacramentum. vii