The first Christian writings preserved the memory of apostolic times, in their narrative and doctrinal dimensions and their reflection upon Jesus and his gospel. The first communities were diverse – they varied in culture, ritual practices, and writings used; different doctrines existed. Christological and theological thinking advanced, notably in the 2nd and 3rd centuries, with the development of exegetical schools (the two most important being Antioch in Syria and Alexandria in Egypt), and the debates raised among themselves and between different Christian communities. Meanwhile, the aspiration to unity emerged. As the canon was gradually established, so was the body of doctrines steadily developed, along with the opposite concepts of “orthodoxy” and “heresy”. In the absence of a central authority, this development stemmed from the interaction of the bishops (see the section “Authority, ministers of worship”), whose growing power began in the 2nd century, and who claimed their legitimacy from their succession in a line going back to the apostles. Christianity’s legalization under Constantine provided the ability to hold ecumenical councils (a conference of Church ministers to define dogma and rule on disciplinary matters; they are ecumenical when they assemble ministers from all inhabited parts of the Roman world, oikoumenè in Greek) in order to discuss and make decisions. These councils were supported by the emperors, who felt concerned by the threats to the unity of the Empire posed by doctrinal conflicts that were often the product of local distinctions, social cleavages, and cultural differences. Nonetheless, it took several councils in the 4th and 5th centuries to impose a body of doctrines.
The first of these councils was convened by Constantine at Nicaea in 325. Its purpose was to address matters of Church discipline, namely to set the date of Easter; and to resolve dogmatic issues, specifically relating to the relation between the Father and the Son. Moving against Arius, an Alexandrian priest who believed that solely the Father was uncreated and that the Son was subordinate, the Council of Nicaea recognized their equality by introducing the Greek term homoousios (translated in Latin as consubstantia), and it produced a profession of faith which listed the fundamental tenets that all Christians were to embrace in heart and mind.
A second council, which met in Constantinople in 381, confirmed the Nicene Creed and expanded on it. Its text was called the Credo (or the Nicene-Constantinopolitan Creed), and an imperial decree declared that all Christians were to proclaim it as their profession of faith. Those who refused were denounced for not to holding Christian truth and were expelled from the communion (excommunicated).
Discussions did not conclude with this council, however, and they subsequently bore on the nature of Christ. These centered around two schools, that of Alexandria (Christ had one nature that is divine), and that of Antioch (two natures, human and divine, undivided in one person). The third council, which was convened at Ephesus in 431, condemned Nestorius (who held that the two natures of Christ were disunited, superimposed); and the fourth one, at Chalcedon in 451, reaffirmed the Credoand ruled that Christ had two natures neither divided nor disunited. Certain Churches in the Mediterranean Orient dissented from these decisions.
These first four councils are still recognized today by the Catholics, the Orthodox and the vast majority of Protestants. Over time, other dogmas were added to the body of doctrines contained in the Credo, but these were not accepted by all Christians. They include, for Catholics, the dogma of the Immaculate Conception (1854), which states that Marian conception is preserved from the original sin; the dogma of papal infallibility (1870); and the dogma of the Assumption of the Virgin (1950), whereby “at the end of her earthly life”, Mary was raised into heaven.