Reformation

A major religious, political, and cultural movement in 16th-century Europe that sought to reform the doctrines, practices, and structure of the Roman Catholic Church. It began with figures such as Martin Luther, John Calvin, and Huldrych Zwingli, who challenged papal authority, the sale of indulgences, and certain church doctrines, emphasizing instead the authority of Scripture (sola scriptura), justification by faith alone (sola fide), and salvation by God’s grace. The Reformation led to the establishment of various Protestant denominations, such as Lutheranism, Calvinism, Presbyterianism, Zwinglianism and Anglicanism, and profoundly transformed Christian theology, worship, education, and European society. The term derives from the Latin reformatio, meaning “restoration” or “renewal”.

Reformed

Term that refers to both the theological doctrines and the churches that emerged from the 16th-century Protestant Reformation, particularly shaped by figures such as John Calvin and Huldrych Zwingli; Reformed doctrines emphasize the sovereignty of God, predestination, covenant theology, salvation limited to the elect, and the spiritual presence of Christ in the Lord’s Supper, while Reformed churches adhere to these teachings and are typically governed along representative or Presbyterian lines, reflecting a systematic renewal of church beliefs and practices according to Scripture.

Revelation

The last canonical book of the New Testament that describes an apocalyptic prophecy. It is considered to be one of the most controversial and difficult books of the Bible, so much so that it was the only book of the New Testament on which John Calvin did not write a commentary. Since the author of Revelation identifies himself as John, many in the past have thought that the Apostle John was its author. Nowadays, many question this authorship due to the many inconsistencies in grammar and style between the Gospel of John and the book of Revelation. Textual evidence has made it clear that the author of the latter was far less familiar with the Greek language than the Gospel's author. Since the author was on the island of Patmos when he received his visions, he is generally referred to as John of Patmos.

Roman Catholic Church

The largest Christian church, headed by the Pope in Rome, with a hierarchical structure of bishops, priests, and deacons. It teaches that it is the one true Church founded by Jesus Christ, emphasizing the authority of Scripture and Sacred Tradition, the sacraments as means of grace, and the role of the Pope as the successor of Peter. The term “Catholic” comes from the Greek katholikos (καθολικός), meaning “universal,” reflecting the Church’s self-understanding as the universal body of Christ. The designation “Roman” indicates the Church’s central governance in Rome and its allegiance to the Pope, distinguishing it from other Christian traditions. The Roman Catholic Church traces its origins to the community of believers founded by Jesus Christ and his apostles in the 1st century AD, particularly to the apostle Peter, whom Catholics regard as the first Bishop of Rome and the Church’s spiritual foundation. Over time, the Church developed as the central institution of Western Christianity, formally organized around the papacy in Rome. By the 4th century, following Emperor Constantine's legalization of Christianity under the Edict of Milan (313 AD) and the establishment of Christianity as the state religion of the Roman Empire under Theodosius I (380 AD), the Church gained significant political and social influence. During the early Middle Ages, the Roman Catholic Church became the dominant religious authority in Europe, shaping law, education, and culture. The Great Schism of 1054 marked the division between the Western (Roman Catholic) and Eastern (Orthodox) Churches, largely over issues of papal authority and theological interpretation. In the 11th to 15th centuries, the papacy reached the height of its temporal power but also faced internal crises, such as the Avignon Papacy (1309–1377) and the Western Schism (1378–1417), when multiple popes claimed legitimacy. The Protestant Reformation in the 16th century challenged the Church’s authority and doctrines, leading to the formation of Protestant denominations. In response, the Council of Trent (1545–1563) initiated the Counter-Reformation, reaffirming Catholic teachings, reforming clerical practices, and strengthening ecclesiastical discipline. Through subsequent centuries, the Roman Catholic Church remained a major global institution, influencing politics, education, art, and philosophy. The First Vatican Council (1869–1870) defined papal infallibility, and the Second Vatican Council (1962–1965) modernized church practices, promoting engagement with the contemporary world. Today, the Church remains the largest Christian denomination, with the Pope as its supreme head and the Vatican City as its spiritual and administrative centre.