The council was convoked to help the church respond to the challenge posed by the Protestant Reformation, which had begun with Martin Luther decades earlier.
Heresies about the Sacraments or de fide doctrines which had been rejected or re-defined by the Protestants were specified and assigned automatic excommunication for Catholics who held them.
These canons still apply today, as evidenced by the fact that the contemporary Catechism of the Catholic Church cites them as authoritative on almost every page.
Martin Luther, John Calvin and other prominent Protestants rejected the Catholic belief that a person needs to do good works to attain salvation, teaching that faith alone is sufficient.
The Catholic Church has seven sacraments: baptism, confirmation, the Eucharist, Penance, anointing of the sick, holy orders and matrimony.
The church historically taught that the sacraments, existing in physical places and circumstances, gave invisible grace to the souls of those who received them with the proper disposition and were by no means symbolic.
The Eucharist, also known as Holy Communion or the Blessed Sacrament, is bread and wine which are consecrated during Mass and transubstantiated into the body and blood of Christ.
The church also historically gave communion to children only when they reached the age of reason, and this practice is still followed today.
The Eastern Orthodox church distributed communion to infants (as it still does), and some Protestants questioned the Catholic doctrine.
Although it was almost exclusively given to those soon to die, in modern times it is frequently given to those who are seriously ill (e.g., before major surgery) to prepare them with God's help.
Holy orders in the Catholic Church is the sacrament which makes a baptized man a deacon, priest or bishop.