Joe Carter, in an article entitled “9 Things You Should Know About the Council of Trent” found writes:

Yesterday marked the 450th anniversary of the closing of the Council of Trent, one of the most significant series of meetings in Christian history. Here are nine things evangelicals should know about the Council and the decrees that it issued:

1. The Council of Trent was the most important movement of the Catholic Counter-Reformation, the Catholic Church’s first significant reply to the growing Protestants Reformation. The primary purpose of the council was to condemn and refute the beliefs of the Protestants, such as Martin Luther and John Calvin, and also to make the set of beliefs in Catholicism even clearer. Approximately forty clergymen, mainly Catholic bishops, were in attendance during the twenty-five times over the next eighteen years that the Council convened.

2. Protestants endorse justification by faith alone (sola fide) apart from anything (including good works), a position the Catholic Church condemned as heresy. During the the sixth session, the Council issued a decree saying that, “If any one saith, that the justice received is not preserved and also increased before God through good works; but that the said works are merely the fruits and signs of Justification obtained, but not a cause of the increase thereof; let him be anathema.”

3. The Protestant Reformers rejected the Apocrypha as part of the biblical canon. (The term Apocrypha (Gr., hidden) is a collection of ancient Jewish writings and is the title given to these books, which were written between 300 and 30 B.C., in the era between the Old and New Testaments.) During the the fourth session, the Council issued a decree damning anyone who rejected these books:

. . . if any one receive not, as sacred and canonical, the said books entire with all their parts, as they have been used to be read in the Catholic Church, and as they are contained in the old Latin vulgate edition; and knowingly and deliberately contemn the traditions aforesaid; let him be anathema.

Many doctrines unique to Catholicism, such as the teachings of purgatory, prayers for the dead, and salvation by works, are found in these books.

4. During the Protestant Reformation, the doctrine of transubstantiation was heavily criticized as an Aristotelian “pseudophilosophy.” The 13th session reaffirmed and defined transubstantiation as “that wonderful and singular conversion of the whole substance of the bread into the Body, and of the whole substance of the wine into the Blood – the species only of the bread and wine remaining – which conversion indeed the Catholic Church most aptly calls Transubstantiation.”

5. Protestants claimed that the only source and norm for the Christian faith was Holy Scripture (the canonical Bible without the Apocrypha). The doctrine of Sola Scriptura was rejected at Trent. The Council affirmed two sources of special revelation: Holy Scripture (e.g., all the books included in the Latin Vulgate version) and traditions of the church (including the “unwritten traditions”).

6. In Catholic theology, an indulgence is a remission of temporal punishment due to sin, the guilt of which has been forgiven. Under Catholic teaching, every sin must be purified either here on earth or after death in a state called purgatory. The selling of indulgences was not part of official Catholic teaching, though in Martin Luther’s era, the practice had become common. (Luther was appalled by the sermon of an indulgence vendor named John Tetzel who said, “As soon as the coin in the coffer rings, the soul from purgatory springs.”) The Council called for the reform of the practice, yet damned those who “say that indulgences are useless or that the Church does not have the power to grant them.”

7. In Catholic theology, purgatory is a place or condition of temporal punishment for those who denied yet were not free from “venial” sins (a lesser sin that does not result in a complete separation from God and eternal damnation in hell). The council affirmed the doctrine of purgatory and damned anyone who claimed “that after the grace of justification has been received the guilt is so remitted and the debt of eternal punishment so blotted out for any repentant sinner, that no debt of temporal punishment remains to be paid.”

8. In the 24 session, the council issued decrees on marriage which affirmed the excellence of celibacy, condemned concubinage, and made the validity of marriage dependent upon the wedding taking place before a priest and two witnesses. In the case of a divorce, the right of the innocent party to marry again was denied so long as the other party was alive, even if the other party had committed adultery.

9. At the request of Pope Gregory XIII, the Council approved a plan to correct the errors to the Julian calendar that would allow for a more consistent and accurate scheduling of the feast of Easter. The reform included reducing the number of leap years in four centuries from 100 to 97. Although Protestant countries in Europe initially refused to adopt the “Gregorian calendar” (also known as the Western or Christian calendar), it eventually became the most widely accepted and used civil calendar in the world.

(Note: The declarations and anathemas of the Council of Trent have never been revoked. The decrees of the Council of Trent are confirmed by both the Second Vatican Council (1962-1965) and the official “Catechism of the Catholic Church” (1992).)