Despite Luther and other reformer’s appeals for a universal council, during the early years of the 16th century the popes opposed the notion for fear of the reemergence of the conciliarist movement in the Roman Catholic Church. Finally, it was Pope Paul III who convoked an assembly, though it was not a universal council, ultimately only including Roman Catholic prelates. Once gathered, its end was “the uprooting of heresy, the restoring of peace and unity, and the reformation of ecclesiastical discipline and morals”, and so began the Counter Reformation.
The Roman Catholic doctrine of justification was not defined until after the beginning of the reformation at the Counter Reformation. The Roman Catholic Church’s response to Protestantism was three-pronged and included the Spanish Inquisition, the founding of the Jesuit Order, and the Council of Trent. It is interesting to note the proclamations of the Council of Trent were reaffirmed in toto in the Roman Catholic catechism in the 1990’s, so the Roman Catholic Church officially still affirms the canons of Trent.
The council, in Canons on the Sacraments in General, asserts the assembly is “lawfully assembled in the 
Holy Spirit”, and is “adhering to the teaching of the Holy Scriptures, to the apostolic traditions, and to the unanimous teaching of other councils and of the Fathers”. Being in unity with the Holy Spirit and adhering to the teaching of Scripture, apostolic traditions, past councils, and the teachings of early church Fathers are all cited as justification for the authority of the Council of Trent.
Ultimate importance is given to what is dubbed the “most holy sacraments of the church”. If anyone changes the quantity or quality of the seven sacraments (Canon 1), says they are not necessary for salvation (Canon 4), says they are merely outward signs of grace conferred and do not in themselves confer grace (Canon 6 & 7), or says all Christians have the power to administer them (Canon 10), then those people are to be anathema (accursed).
With regard to origin, the sacraments were all instituted by Jesus Christ himself (Canon 1). They are significant because they are necessary for salvation (Canon 4) and directly contain the grace which they also outwardly signify (Canon 6 & 7). Many of the canons are in direct contrast with Protestant reforms, including the canons decreeing there are seven specific sacraments instead of two sacraments (Canon 1), justification is not obtained by grace through faith alone (contrasting sola fide, sola gratia) but requires the administration of the sacraments (Canon 4), the sacraments literally contain the grace they signify to confer (Canon 6 & 7), grace is not conferred by faith alone (contrasting sola fide, sola gratia) in the divine promise but ex opere operato (the sacraments derive their power from Christ’s work and are independent of the recipient’s faith) (Canon 8), and (Sacerdotalism instead of Universal Priesthood) not all Christians can administer the Word and sacraments (Canon 10).
In the Index of Prohibited Books, any books written by or New Testaments translated by Luther, Zwingli, Calvin, Balthasar Friedberg, Schwenkfeld, and others like them were condemned as heretical and forbidden. Books are condemned either by the Pontiff or by ecumenical councils, and inspections can be done by bishops, inquisitors, and Roman Catholic theologians. Different translations of the Old Testament may be read by pious men only, at the discretion of the local bishop. The Vulgate edition is the preferred and official version of the Roman Catholic Church. Book dealers selling or supplying Bibles written in vernacular languages will be fined and punished. Bishops, inquisitors, and theologians are the ones primarily in charge of controlling what books are available to people, and it makes sense to focus so much on books since they are storehouses of information (and increasingly widespread with the printing press).