The first council of Constantinople was convened in 381 A.D. in—guess where?—Constantinople. It was convened by Theodosius, with the goal of uniting the church upon the basis of the orthodox faith. But travel was difficult at that time, and despite Theodosius’ good intentions, the council was poorly attended—with no Western bishops or legates in attendance. Only a few bishops from Egypt attended, and they arrived late. In reality, then, the council was only a synod of bishops from Thrace, Asia and Syria.
Considering its sectional character, Constantinople I may not have been listed among the great “ecumenical” councils at all; but eventually, its doctrines were affirmed by the entire Christian church, and the Council came to be regarded as ecumenical by both the West and the East.
Core Teachings—Most importantly, Constantinople I reaffirmed the tenets of the faith which were delineated in Nicaea, and denounced all opposing doctrines. The divinity of the Holy Spirit was an important issue, as the Church debated and formalized its emerging understanding of the Trinity.
The so-called “Niceno-Constantinopolitan Creed”, generally ascribed to this council, is probably a Jewish baptismal formula revised by interpolation of a few Nicene test-words. More recently, its claim to be called ”Constantinopolitan” has been challenged; scholars note that the creed is not found in the earliest records of the acts of the council, nor was it referred to by the later Council of Ephesus (431 A.D.), nor by the “Robber Synod (449 A.D.)—although both of these councils affirmed the Nicene faith. Nonetheless, it is this creed which became the creed of the universal church—and it has been retained without change, except for the addition of filioque.
Filioque—Latin for “and from the Son,” the word filioque (pronounced fee-lee-OH-kway)—is foundational to Christian belief, in that it defines the three persons of the Trinity: the Father, the Son, and the Holy Spirit. In the original Greek form, the creed said that the Holy Spirit proceeds “from the Father.” With the inclusion of the “filioque,” the Church clarified that the Holy Spirit proceeds from both the Father and the Son.
Et in Spiritum Sanctum, Dominum, et vivificantem: qui ex Patre Filioque procedit.
(And in the Holy Spirit, the Lord, and giver of life, who from the
Father and the Son proceeds.)