A letter some early Christians counted as scripture never made the New Testament
Around the year 96, Clement of Rome wrote to squabbling Christians in Corinth urging harmony. Some early churches treated that letter as part of the Bible, and even in the 14th century Ibn Khaldun listed it with the New Testament. Clement was among the Church Fathers, the thinkers who shaped Christian doctrine for seven centuries.
The Patristic Era runs roughly from the late 1st to the mid-8th century and peaked in the 4th and 5th, as Christianity became the state church of the Roman Empire. Many denominations treat the Fathers' writings as part of Sacred Tradition and authoritative for doctrine, although there is no fixed list, and even major contributors such as Origen and Tertullian had parts of their teaching condemned later.
The earliest group, the Apostolic Fathers, lived in the 1st and 2nd centuries and are believed to have known some of the apostles or been shaped by them. Besides Clement, the chief figures are Ignatius of Antioch, who wrote a string of preserved letters on bishops and sacraments while being taken to Rome for martyrdom, and Polycarp of Smyrna, said to be a disciple of John, who unsuccessfully urged the Roman bishop Anicetus to adopt the Eastern date for Passover and was put to death around AD 155. His own pupil Irenaeus, bishop of Lyon, attacked heresies in his book of about 180 and argued that the four gospels should all be accepted as canonical.
Alexandria produced some of the boldest minds. Clement of Alexandria tried to reconcile Greek philosophy with the faith, founding what scholars call Christian philosophical theology. Origen corrected the Greek Old Testament using Hebrew, commented on every book of the Bible and suggested that all creatures, perhaps even fallen angels, might one day be restored to God. Three centuries after his death, a council in 553 condemned the so-called Origenist errors.
The 4th century was dominated by the fight over Arianism, the teaching that Christ was of a different substance from the Father. Athanasius argued against it at the Council of Nicaea in 325. The Cappadocian Fathers, the brothers Basil the Great and Gregory of Nyssa with their friend Gregory of Nazianzus, raised in a household guided by their sister Macrina, won back moderates with the formula of three persons in one essence, feeding into the Trinity defined at Constantinople in 381.
Source: Church Fathers
