The underlying beliefs of the Roman Catholic Church, such as the existence of the Holy Trinity, the resurrection of Jesus and the rite of baptism as a necessity for salvation, are seen by the Church as divinely revealed truth and unchangeable. However, some customs and teachings have changed over the centuries, such as whether priests can marry, abstaining from meat on Fridays and presenting the mass in Latin.
Changes in society and interpretation of scripture have led certain teachings of the Roman Catholic Church to evolve over time. The Church once forbade usury, the charging of interests on loans, but now permits the practice. The practice of slavery, once condoned, was condemned when the Church recognized enslaved people as fully human.
Customs within the Church have evolved over time as well. In the early Church, married men could be ordained as priests. The Church changed this practice in the 10th century, and now candidates for the priesthood must be unmarried and celibate.
The Second Vatican Council, or Vatican II, held in the early 1960s, made many changes to the practices of the Church. Before the council, masses around the world were held in Latin. Vatican II changed the language of the mass to the vernacular of the local community. The laity were also given an increased role in the Church, which up to that time was a strict hierarchy.