Martin Luther's 95 Theses
The Counter-Reformation began in the 16th century as an internal effort to reform the Catholic Church. It has also been interpreted as a reaction to the Protestant Reformation. There was already dissatisfaction with the Catholic Church when Martin Luther’s 95 Theses sparked further criticism of the Church and spread the Protestant Reformation across Europe.

Luther’s 95 Theses were a series of arguments against the practices of the Catholic Church—specifically against the sale of indulgences and the belief in salvation only through a combination of both faith and good works. Although some scholars debate whether Luther actually posted his 95 Theses on the doors of Castle Church in Wittenburg in 1517, the 95 Theses were soon printed and disseminated throughout Europe.  

In the early 16th century, the pope began to take measures to reform the church. In 1540, he established the Society of Jesus, a religious order whose members would become the leaders of reformed Catholicism. In 1545, the Council of Trent brought together church leaders from all over Europe to establish major reforms in the Church. 

The Council of Trent 
The Council of Trent was composed of 25 sessions that met between 1545 and 1563. At the meetings, leaders focused on two things: reforming corruption in the Church and affirming religious doctrines. They established guidelines to clean up corruption and apathy among church leaders and banned the selling of indulgences. They also clarified the beliefs of the Church. The Council based its decrees on both scripture and tradition, and it became clear that there were fundamental differences between Catholicism and Protestantism. For example, the Council affirmed that unlike Protestant belief, Catholics did not stand alone before God. Thus, prayers to saints and to the Virgin Mary were deemed important in attaining salvation. The Council also declared that within Catholicism, both faith and good works are necessary for salvation. 

Transubstantiation vs. Consubstantiation
The specific nature of communion is a key difference between the Protestant and Catholic churches that was clarified by the Council. The Council of Trent confirmed the Catholic belief in transubstantiation, in which the wine and bread of the Eucharist during communion literally become the blood and body of Christ. Protestants, on the other hand, believe in consubstantiation, in which the wine and bread of the communion ritual are merely symbolic. 

Decrees on Works of Art
Because the Catholic Church wanted to reach the widest audience possible, the Council of Trent declared that the Church should use art to communicate religious themes. Church leaders recognized that visual representations of biblical stories, the saints, and the life of Jesus could create direct and emotional involvement in the Church. Thus, the Roman Catholic Church supported the drama and realism of the Baroque style of art.