What is the difference between the Orthodox, Catholics and Protestants, and which beliefs do they share?
Answer: (1) Orthodox Christianity and the Catholic Church
The term Orthodox Churches refers to those Churches who live Christianity in the form it had developed in Byzantine times. This form developed in the eastern part of the Roman Empire and went beyond the boundaries of the Empire, especially into East Slavia. Many Oriental Orthodox Churches also claim the name Orthodox Church for themselves. They differ from the Orthodox Churches in their liturgy and doctrines (although a congruence concerning the dogmatic differences, especially the Christological questions, was reached in 1980). The Catholic Eastern Churches differ in their canonical unity with the Bishop of Rome. The term orthodox, which is often translated as of the right faith, really means praising (God) in the right way, and thus points to the central importance of the liturgical dimension in the life of the Orthodox Churches.
For the Orthodox Churches, the primacy of the Bishop of Rome (see the text introducing the Theme ”The Church”, part III) is still the main reason for retaining the separation of the Churches initiated in 1054 AD. The spreading of the Primacy in the West was, however, not largely due to the Roman desire for power, but to the responsibility for the freedom and the unity of the Church. This primacy was more given to Rome by others, rather than demanded by Rome itself. To legitimize the split, a number of theological issues were and are still cited, for example the rejection of the Latin customs of unleavened bread during the celebration of the Eucharist, the celibacy of priests, or a slightly different wording in the creed which is known as the Filioque clause.
Along with these decisive reasons for the split into the Orthodox and the Roman Catholic Church, different styles of worship and of spirituality also come into play, so that it is not so much the doctrinal differences, but more the way of being a Christian, which have always been the major difference between East and West and are still so today.
The continued existence of the Roman Empire in the East meant the continuation of the empires Church, which was founded by Emperor Constantine (reigned 306-337). The emperor was celebrated as Gods representative on earth. He was a Christ-like, western priest-emperor, bearer of all rights and standing above even the laws of the Church (the Canon Law). His power in the Church, for the development of its doctrines, laws and administration were limited only by God’s law. In this system, which has not always correctly been called caesaropapism, the people and the Church, as well as Church and State were linked as closely as possible. The patriarchs stood markedly below the emperor and often acted according to his orders. This Church structure continued after the fall of the East Roman empire which was replaced by national rulers, such as the czars of Russia, or the Serbian and Romanian rulers. In all these instances, the result was an independent patriarchy. The practicing of religion was largely limited to the liturgical and remained there unchanged for centuries. There were no major innovations, not in the area of theology nor that of Christian philosophy, political science or art. The Church continued to exist as though time had stood still.
The developments in the West were very different. After the fall of the Western Roman Empire, the Pope emerged strengthened and eventually as representing the only remaining intact ruling body. Subsequently, he provided the spiritual leadership for Middle and Western Europe and thus became a kind of supra-national link between the Church provinces, and was asked by local and regional rulers to legitimize their claims to power. While in Eastern Europe the king stood above the patriarch and protected him, the balance of power in the West appeared to be exactly the opposite.
Not least because of the Investiture Controversy and its solution, the Western system eventually resulted in the separation of the political and the religious. The importance of this for the development of Western philosophy cannot be emphasized highly enough. Neither Eastern Europe nor the Islamic world have developed anything comparable and therefore remain, as regards this issue, at the same level of development they had reached at the beginning of the medieval times. Only Western Europe moved on from this and dared to enter a new era, pushed forward by the continuous battle for supremacy of the two very different blocks of power, that of the Church and that of the king.
(The previous five paragraphs are largely taken from Peter Antes, “Mach’s wie Gott, werde Mensch. Das Christentum”. Düsseldorf: Patmos, 1999. S. 110-112.)
(2) The Protestant Reformation and the Catholic Church
The deplorable state of affairs in Rome at the time of the Renaissance, in the Bishops palaces and among the uneducated clerics (from the 14th century) was for many in the Western Church a call for a complete reform. Because of the wars, which often served the interest of the ecclesiastical princes, the plague and periods of rampant hunger, as well as the almost continuous threats of hell fire, the population at large lived in great fear. Many people took to pilgrimages, worshipping relics and paying indulgences, which were often linked to a belief in magic and taken advantage of by pardoners.
Prepared by attempted reforms by J. Wyclif (died 1384) and J. Hus (died 1415), Martin Luther’s (died 1546) criticism of the prevailing situation, which obscured the doctrine of Justification by Faith, fell on fertile ground; it was promoted by the circulation of his writings and his translation of the original texts of the Bible by means of the printing press. Intensified by the political ambitions of the ecclesiastical princes and the lack of real understanding in Rome, Martin Luther’s attempts at reforming the Church led instead to the second large schism, which resulted in the separation of the reformed branch under U. Zwingli (died 1531) and J. Calvin (1564), and a little later also the secession of the Anglican Church.
As a reaction to the previous disregard for the Bible, as well as overestimating the importance of good deeds, these Churches attempted to draw solely on the Spirit of Holy Scripture (“sola scriptura”), trusting in God's grace (“sola gratia”) to give glory to God alone (“solus Deus”). While the reformers, in spite of their criticism of the Roman Church, were still very much linked to the traditions of the Church (e.g. they still based their teachings on the old Councils), this changed during the subsequent decades. "Protestant Orthodoxy" (17th century) recognized virtually only the Bible as providing guidance for a Christian life, and they consider it to be wholly inspired by God - even down to the last comma. The term "Protestants" was first coined by these churches themselves as late as in the mid-16th century in England.
The Catholics, who had remained loyal to Rome, took up the calls for renewal by means of the Catholic Reform (esp. the Council of Trent, 1545-1563) and endeavoured to put an end to all the prevailing shortcomings and to renew Christian life by means of good ordination training for priests, bishop visitations, encouraging true reverence of saints, Eucharistic piety, etc. However, just like the implementation of the Reformation, the Catholic Reform was often marked by violence. In connection with the Catholic Reform, which finds its reflection in the arts in the buildings, paintings and writings of the baroque period, the discovery of new continents eventually resulted in a major missionary movement. This also led for the first time to a more intense encounter with other religions.