I have been reading more of William Jurgens' Faith of the Early Fathers. St. Cyprian (ca. 200 -258) was bishop of Carthage; he survived the Decian persecution but ultimately was martyred by beheading. Among his writings are passages about the Eucharist. One of his letters ("To a Certain Cecil," 63, 9) indicates the nature of Catholic sacramental theology in which a certain form and matter is necessary. The form is the words or actions being said or performed, and the matter is the material used in the sacrament. For example, in baptism the form is the Trinitarian formula: "I baptize you in the name of the Father, and of the Son, and of the Holy Spirit." (That is why last year the Vatican re-affirmed the teaching that baptisms not using the Trinitarian form are not valid.) The matter in baptism is the water.
In the Eucharist, the form is the Eucharistic prayer, and the matter is the bread and wine (mixed with water). Cyprian addresses a practice of using water instead of wine, rather than wine mixed with water:
We find that the cup which the Lord offered was mixed; and that what was wine, He called Blood. From this it is apparent that the Blood of Christ is not offered if there is no wine in the cup; nor is the Sacrifice of the Lord celebrated with a legitimate consecration unless our offering and sacrifice corresponds to the passion... I wonder, indeed, whence this practice has come, that, contrary to evangelic and apostolic tradition, in certain places water alone, which cannot signify the Blood of Christ, is offered in the cup of the Lord. (Faith of the Early Fathers, Volume 1, #582, p. 232).
Because the matter used does not conform to the matter required (no wine is used) in accord with the "evangelic and apostolic tradition," the sacrament does not take place. We cannot simply make it up as we go along. The power of the sacraments comes from the One who instituted them, and the One who instituted them knew that the physicality of the sacraments (and thus how the sacraments signify what they effect) matters. When we are tempted to think that the Church has too many rules about things, it is important for us to remember the reasons why she has such rules. Again, we see the truth of lex orandi, lex credendi (literally, "the law of praying, the law of believing"). What the phrase means is that the way we worship affects how we believe, so orthodox worship leads to orthodox belief and theology. It is also true that heterodox worship leads to heterodox belief and theology. So in our liturgy and in our sacraments, what we say and do has far-reaching consequences.