First seven Ecumenical Councils in the context of "Chalcedonian Definition"

Christianity in the 4th century was dominated in its early stage by Constantine the Great and the First Council of Nicaea of 325, which was the beginning of the period of the First seven Ecumenical Councils (325–787), and in its late stage by the Edict of Thessalonica of 380, which made Nicene Christianity the state church of the Roman Empire.

The Chalcedonian Definition (also called the Chalcedonian Creed or the Definition of Chalcedon) is the declaration of the dyophysitism of Christ's nature, adopted at the Council of Chalcedon in AD 451. Chalcedon was an early centre of Christianity located in Asia Minor. The council was the fourth of the ecumenical councils that are accepted by Chalcedonian churches which include the Catholic and Orthodox churches.

It was the first council not to be recognised by any Oriental Orthodox church; for this reason these churches may be classified as Non-Chalcedonian.

The doctrine of the Trinity, considered the core of Christian theology by Trinitarians, is the result of continuous exploration by the church of the biblical data, thrashed out in debate and treatises, eventually formulated at the First Council of Nicaea in AD 325 in a way they believe is consistent with the biblical witness, and further refined in later councils and writings. The most widely recognized Biblical foundations for the doctrine's formulation are in the Gospel of John, which possess ideas reflected in Platonism and Greek philosophy.

Nontrinitarianism is any of several Christian beliefs that reject the Trinitarian doctrine that God is three distinct persons in one being. Modern nontrinitarian groups views differ widely on the nature of God, Jesus, and the Holy Spirit.