The work of the council was confirmed by Pius IV (in the papal bull Benedictus Deus, 1564), and its most important prescription, the issuance of an explicit account of the beliefs of the church, was fulfilled by the publication (1566) of the Catechism of the Council of Trent, or Roman Catechism (which, in fact, was not catechetical but descriptive in form). The dogmatic definitions and the reform decrees of the first group of sessions treated the Scriptures (canon, text, interpretation, and function), original sin, justification, the sacraments in general, baptism, and confirmation; and also the regulation of education, preaching, and alms collecting and the duties and obligations of bishops and beneficiaries. The canons on justification (6th session), the product of seven months of discussion, are among the chief work of the council.
The second period of the council was notable for the work of the Jesuits, especially Diego Lainez. The subjects treated were the Eucharist, penance, extreme unction, episcopal jurisdiction and office, clerical discipline, and benefices. The third period was dominated by St. Charles Borromeo; its definitions and regulations covered communion in both kinds, the Mass, the sacraments of orders and matrimony, the veneration and invocation of the saints, the cult of relics and images, the list of forbidden books, the priesthood in all its phases, ecclesiastical foundations, education, marriage, religious orders, feasts and fasts, and the service books of the church.