Although the First Council of Nicaea had condemned the Arian belief and reasserted the dogma that the Father and the Son were of the same substance, some theologians believed that the Holy Spirit, the third Person of the Trinity, differed in substance from the other two Persons, being a kind of 'creature' of the second Person. This heresy was called Macedonianism.

 

In May 381 a second Ecumenical Councils was summoned by Theodosius I (378-395) to meet in Constantinople in the church of Hagia Irene to define the nature of the Holy Spirit. He had recognized Christianity as the official religion of his empire a year before. The emperor had done his homework carefully and already instructed the Churches that the object of the council would be the reconfirmation of the Nicene Creed. This time no representatives came from Rome.

The council reaffirmed the Nicene faith in the sense that it reasserted the keywords 'of the same substance', or homoousios and that the Holy Spirit was of the same substance with the Father and the Son. This council brought an end to Arianism, which had already been split into smaller dissensions, within the empire. It continued on among the Goths, who were converted among many other Arian missionaries by Ulfila (311-83), translator of the Gothic Bible, and among Vandals and Lombards.
The most important decision which concerned the Church hierarchy was that to the vexation of Alexandria- 'the bishop of Constantinople should have rank after the bishop of Rome because it is New Rome.' Thus Constantinople replaced Alexandria which until then had held the second place after Rome and also moved above Antioch and Jerusalem.