<P> In the twenty - fifth and last session, the doctrines of purgatory, the invocation of saints and the veneration of relics were reaffirmed, as was also the efficacy of indulgences as dispensed by the Church according to the power given her, but with some cautionary recommendations, and a ban on the sale of indulgences . Short and rather inexplicit passages concerning religious images, were to have great impact on the development of Catholic Church art . Much more than the Second Council of Nicaea (787) the Council fathers of Trent stressed the pedagogical purpose of Christian images . </P> <P> The council appointed, in 1562 (eighteenth session), a commission to prepare a list of forbidden books (Index Librorum Prohibitorum), but it later left the matter to the Pope . The preparation of a catechism and the revision of the Breviary and Missal were also left to the pope . The catechism embodied the council's far - reaching results, including reforms and definitions of the sacraments, the Scriptures, church dogma, and duties of the clergy . </P> <P> On adjourning, the Council asked the supreme pontiff to ratify all its decrees and definitions . This petition was complied with by Pope Pius IV, on 26 January 1564, in the papal bull, Benedictus Deus, which enjoins strict obedience upon all Catholics and forbids, under pain of excommunication, all unauthorised interpretation, reserving this to the Pope alone and threatens the disobedient with "the indignation of Almighty God and of his blessed apostles, Peter and Paul ." Pope Pius appointed a commission of cardinals to assist him in interpreting and enforcing the decrees . </P> <P> The Index librorum prohibitorum was announced in 1564 and the following books were issued with the papal imprimatur: the Profession of the Tridentine Faith and the Tridentine Catechism (1566), the Breviary (1568), the Missal (1570) and the Vulgate (1590 and then 1592). </P>

Why was the council of trent so important to the church