This paper, as much provocative as it is nostalgic, starts from the thesis of the Vatican II Constitution on the Sacred Liturgy, Sacrosanctum Concilium, that "the Church recognizes Gregorian chant as proper to the Roman liturgy" (SC 116). Given the practical disappearance of chant practice in the Church and the accompanying emergence of ever new forms of ecclesiastical musical expression, the question arises as to the meaning and role of chant today. Being itself a synthesis of synagogue and Greek traditions, for many centuries it was—at least theoretically—the cultural, but also social, and one might even say political, bond of the Church. In that period, in a certain sense, it "sufficed" for the fullness of the Church's musical expression, resonating with theological thought and the plastic arts, at least as a kind of universal ideal. With the development of modern music, chant becomes the matrix for the Western tonal system, and its motifs and forms continue to inspire to this day. Comparing its idiom (inspiration drawn from spiritual experience /lectio divina/, the absolute priority of the word in its organic bond with melody, modality) with the evolving explorations of forms of sacred music makes it possible to shed light on the direction in which contemporary sacred music is heading, while proposing a model for "measuring" its "catholicity"—understood here as the highest artistic, universal quality, verified over the centuries. The set of parameters of chant's universality proposed in this way can become a kind of measure of the "quality" and thus of the "catholicity" of today's sacred music. These reflections, based on historical and musicological arguments, develop certain intuitions of Ernest Ansermet contained in his work Les Fondements de la musique dans la conscience humaine.