SOMMARIO: In the absence of any study on the Thesaurus of Gavanti-Merati, even though it was one of the books read most widely by the post- Tridentine clergy, the article deals with the theology of the Mass in so far as it can be drawn out from the commentary of the two authors on the Rubrics of the Missal of St. Pius V. Questions, new and old, are raised: the Liturgy of the Word, eucharistic communion, the altar, processions... discovering new freshness in these genuine pioneers of many aspects of recent theological-liturgical thought.