Already in apostolic times, distortions of belief threatened the Christian community from within. The Apostle Paul needed to correct those who misunderstood the preaching of Christ’s Resurrection and the general resurrection to come (1 Corinthians 15). The First Letter of John combats those who denied the reality of the Incarnation—“that Jesus Christ has come in the flesh” (4:3). Bishop Ignatius of Antioch denounced the same “docetic” tendency—that Jesus only “seemed” (dokein) to be human—when he found heretics abstaining from the Eucharist “because they do not confess that the Eucharist is the flesh of our Saviour Jesus Christ which suffered for our sins and which the Father raised” (Letter to the Smyrnaeans 7:1).

Alternative understandings of Christian teaching continued to develop throughout early church history. Marcion, considered the arch-heretic of the 2nd century, rejected the Old Testament as the work of a god inferior to the God of Jesus and accepted from the nascent New Testament only those portions that he took to be uninfected by Judaism. Bishop Irenaeus of Lyon, in Against Heresies, ranked Marcion with the “gnostics” because at least one facet of Marcion’s error was his depreciation of the material creation. The gnostics invented complex cosmogonies in order to remove the true God from responsibility for the evils of matter, release from which was the content of human salvation. The goodness of the material creation was affirmed for Irenaeus by the reality of Christ’s Incarnation, the sacramental practices of the church (bread and wine made from wheat and grapes), and the Christian hope in the resurrection of the body.

More-subtle threats than the docetic to the humanity of Christ came from the view that the divine Logos—the “Word” or the principle of God active in the creation and the continuous structuring of the cosmos—had taken the place of the human mind or will in Jesus. Apollinaris, whose teaching denied the existence of a rational human soul in Christ, was condemned by the first Council of Constantinople in 381, and monothelitism, which held that Christ had only one will (the divine and not the human), was condemned by the third Council of Constantinople in 680–681. The orthodox teaching was that the Son is a divine person from all eternity who, in the Incarnation, took human nature completely upon himself. Only so could humankind have been saved, for—according to the dictum of Gregory of Nazianzen in the late 4th century—“what had not been assumed would not have been healed” (Epistle 101).

In the other direction, faith in Christ’s divinity was affirmed in the face of early views that made of Jesus a man “adopted” by God, whether at his Resurrection or at his baptism or even already at his conception—views that respectively pressed into service Romans 1:3–4, Matthew 3:16–17, and Luke 1:31–35. It was to exclude such views even in the subtler form they took with Nestorius, bishop of Constantinople—whose emphasis on the full humanity of Christ’s human nature seemingly divided him into two persons, one human and the other divine—that the Council of Ephesus in 431 insisted on the propriety of the popular title “God-bearer” (Theotokos) for Mary.

Even the New Testament’s affirmations of Christ’s preexistence had not sufficed to persuade some of his fully divine status (John 1:1–3; 1 Corinthians 8:6; Colossians 1:15–17). The greatest challenge to the teaching of Christ’s full divinity was that of Arius (early 4th century), who held that the Son, though superior to all other creatures, was in fact God’s first creature. Rejecting that view, the first Council of Nicaea in 325 declared that the Son of the Father—“(true) God from (true) God”—was himself “begotten, not made” and the agent of all God’s creation. This echoed the statement in the Gospel of John (1:3) about the divine Logos, that “without him was not anything made that was made.”

The New Testament writers and the Fathers of the Church had no compunction about identifying false teaching as such. Persistence in it brought expulsion from communion. Many modern scholars have shown more sympathy with so-called heretics, suggesting at least that the controversy inspired by their dissent may have played a useful part in allowing the church to develop and formulate its doctrine. Christians abiding by historical orthodoxy, however, might argue instead that the authentic instinct of faith has never deviated in such fundamental and central matters as the divine status of Christ and the reality of his humanity.

Heresies have survived or reemerged in the course of history: Arianism continued among the Teutonic tribes until the 7th century and in 18th-century England; “adoptionism” reappeared in Spain and France in the 8th and 9th centuries; and antimaterial dualism was revived among the Bulgarian Bogomils in the 10th century and among the Cathars of France and Italy in the 12th. Keen-eyed readers of theological literature can spot contemporary equivalents to most or all of the positions and tendencies mentioned already at the beginning of the 3rd century by Tertullian of Carthage in his treatise On the Prescription of Heretics.