Christianity in the 2nd century in the context of "Early centers of Christianity"

In Christianity, the Great Commission is the instruction of the resurrected Jesus Christ to his disciples to spread the gospel to all the nations of the world. The Great Commission is outlined in Matthew 28:16–20, where on a mountain in Galilee Jesus calls on his followers to make disciples of and baptize all nations in the name of the Father, the Son, and the Holy Spirit.

The Great Commission is similar to the episodes of the commissioning of the Twelve Apostles found in the other Synoptic Gospels, though with significant differences. Luke also has Jesus during his ministry dispatching disciples, including the seventy disciples, sending them to all the nations and giving them power over demons. The dispersion of the Apostles in the traditional ending of Mark is thought to be a 2nd-century summary based on Matthew and Luke.

Traditionally in Christianity, orthodoxy and heresy have been viewed in relation to the "orthodoxy" as an authentic lineage of tradition; other forms of Christianity were viewed as deviant streams of thought and therefore heterodox. This view was challenged by the publication of Walter Bauer's Rechtgläubigkeit und Ketzerei im ältesten Christentum ("Orthodoxy and Heresy in Earliest Christianity") in 1934. Bauer endeavored to rethink early Christianity historically, independent from the views of the current church. He stated that the 2nd-century church was very diverse and included many "heretical" groups that had an equal claim to apostolic tradition. Bauer interpreted the struggle between the orthodox and heterodox to be the "mainstream" Church of Rome struggling to attain dominance. He presented Edessa and Egypt as places where the "orthodoxy" of Rome had little influence during the 2nd century. As he saw it, the theological thought of the "Orient" (in this case the Eastern Roman Empire) at the time would later be labeled "heresy". The response by modern scholars has been mixed. Some scholars clearly support Bauer's conclusions and others express concerns about his "attacking [of] orthodox sources with inquisitional zeal and exploiting to a nearly absurd extent the argument from silence." However, modern scholars have critiqued and updated Bauer's model.

According to Keith Hopkins, the claimed institutional unity of the Christian Church was propaganda constantly repeated by orthodox Christian writers, rather than a genuine historical reality.

The Apostolic Fathers, also known as the Ante-Nicene Fathers, were core Christian theologians among the Church Fathers who lived in the 1st and 2nd centuries AD who are believed to have personally known some of the Twelve Apostles or to have been significantly influenced by them. Their writings, though widely circulated in early Christianity, were not included in the canon of the New Testament. Many of the writings derive from the same time period and geographical location as other works of early Christian literature which came to be part of the New Testament.

Anti-Judaism in Early Christianity is a description of anti-Judaic sentiment in the first three centuries of Christianity; the 1st, 2nd, and 3rd centuries. Early Christianity is sometimes considered as Christianity before 325 when the First Council of Nicaea was convoked by Constantine the Great, although it is not unusual to consider 4th and 5th century Christianity as members of this category as well.

Jewish Christians were excluded from the synagogue, according to one theory of the Council of Jamnia, as they refused to pay the Fiscus Judaicus.

Montanism (/ˈmɒntəˌnɪzəm/), known by its adherents as the New Revelation, was an early Christian movement of the mid-to-late 2nd century, later referred to by the name of its founder, Montanus. Montanism held views about the basic tenets of Christian theology similar to those of the wider Christian Church, but it was labelled a heresy for its belief in new prophetic figures. The prophetic movement called for a reliance on the spontaneity of the Holy Spirit and a more conservative personal ethic.

Montanism originated in Phrygia, a province of Anatolia, and flourished throughout the region, leading to the movement being referred to elsewhere as Cataphrygian (meaning it was "from Phrygia") or simply as Phrygian. They were sometimes also called Pepuzians after the town of Pepuza, which they regarded as the new Jerusalem. Sometimes the Pepuzians were distinguished from other Montanists for despising those not living in the new Jerusalem. The Montanist movement spread rapidly to other regions in the Roman Empire before Christianity was generally tolerated or became legal following the Edict of Serdica in 311. It persisted in some isolated places into the 6th century.

Valentinianism was one of the major Gnostic Christian movements. Founded by Valentinus (b. c. 100 CE – d. c. 165 CE) in the 2nd century, its influence spread widely, not just within the Roman Empire but also from northwest Africa to Egypt through to Asia Minor and Syria in the east. Later in the movement's history, it broke into Eastern and a Western schools. The Valentinian movement remained active until the 4th century, declining after Emperor Theodosius I issued the Edict of Thessalonica in 380, which established Nicene Christianity as the state religion of the Roman Empire.

No evidence exists that Valentinus was labeled a heretic during his lifetime. Irenaeus of Lyons, who was the first patristic source to describe Valentinus's teachings—though likely incompletely and with a bias toward the time's proto-orthodox Christianity—did not finish his apologetic work Against Heresies until the latter 2nd century, likely sometime after Valentinus's death. The rapid growth of the Valentinian Gnostic movement—named eponymously after Valentinus—after his death prompted early Christian thought leaders, such as Irenaeus and later Hippolytus of Rome, to write apologetic works against Valentinus and Valentinianism, which conflicted with proto-orthodox theology. Because the proto-orthodox camp's leadership encouraged the destruction of Gnostic texts writ large, most textual evidence regarding Valentinian theology and practice comes from its critics—particularly Irenaeus, who was highly focused on refuting Valentinianism.

The Old Roman Symbol (Latin: vetus symbolum romanum), or Old Roman Creed, is an earlier and shorter version of the Apostles' Creed. It was based on the 2nd-century idea of the Rule of Faith, a summary of core Christian beliefs, as advanced by such writers as Tertullian and Irenaeus. The declaration of faith for those receiving baptism (3rd century or earlier), which by the 4th century was everywhere tripartite in structure, followed Matthew 28:19 ("baptizing them in the name of the Father and of the Son and of the Holy Spirit"), which is part of the Great Commission.

The Didache (/ˈdɪdəkeɪ, -ki/; Ancient Greek: Διδαχή, romanized: Didaché, lit. 'Teaching'), also known as The Lord's Teaching Through the Twelve Apostles to the Nations (Διδαχὴ Κυρίου διὰ τῶν δώδεκα ἀποστόλων τοῖς ἔθνεσιν, Didachḕ Kyríou dià tō̂n dṓdeka apostólōn toîs éthnesin), is a brief anonymous early Christian treatise (ancient church order) written in Koine Greek, dated by modern scholars to the first or (less commonly) second century AD.

The first line of this treatise is: "The teaching of the Lord to the Gentiles (or Nations) by the twelve apostles". The text, parts of which constitute the oldest extant written catechism, has three main sections dealing with Christian ethics, rituals such as baptism and Eucharist, and Church organization. The opening chapters describe the virtuous Way of Life and the wicked Way of Death. The Lord's Prayer is included in full. Baptism is by immersion, or by affusion if immersion is not practical. Fasting is ordered for Wednesdays and Fridays. Two primitive Eucharistic prayers are given. Church organization was at an early stage of development. Itinerant apostles and prophets are important, serving as "chief priests" and possibly celebrating the Eucharist; meanwhile, local bishops and deacons also have authority and seem to be taking the place of the itinerant ministry.