The idea of faith imputing the merit and righteousness of Christ the Redeemer sprang first from the decrees of the Council of Nicaea concerning three Divine Persons from eternity; and this faith has been accepted by the whole Christian world from that time to the present.
The actual Council of Nicaea was convened by the Emperor Constantine the Great, on the advice of Alexander, Bishop of Alexandria, consisting of all the Bishops in Asia, Africa and Europe, and held in the Emperor's palace at Nicaea, a city of Bithynia*. Its object was to disprove and condemn on the authority of Holy Writ the heresy of Arius, a priest of Alexandria, who was denying the divinity of Jesus Christ. This took place in AD 318**. That assembly reached the conclusion that the three Divine Persons, Father, Son and Holy Spirit, existed from eternity, as can immediately be established by referring to the two Creeds known as the Nicene and the Athanasian. In the Nicene Creed we read:
I believe in one God, the almighty Father, maker of heaven and earth; and in one Lord, Jesus Christ, the Son of God, the only-begotten of the Father, born before all ages, God of God, being of one substance with the Father; who came down from the heavens, and was incarnate by the Holy Spirit of the Virgin Mary; and in the Holy Spirit, the Lord and quickener, who proceeds from the Father and the Son, who together with the Father and the Son is worshipped and glorified.
 The following words occur in the Athanasian Creed:
It is the catholic faith that we revere one God in the Trinity, and the Trinity in unity, neither confusing the Persons nor separating the substance. But as we are compelled by Christian truth to confess each Person separately to be God and Lord, so we are forbidden by the catholic religion to speak of three Gods or three Lords.
This is tantamount to saying that it is allowable to confess three Gods and Lords, but not to speak of them, since this is forbidden by religion, while truth dictates that there are three. This Athanasian Creed was written immediately after the Council had met at Nicaea by one or more people who had taken part in it. It was also accepted as an oecumenical or catholic document. It is plain from these quotations that it was then decreed that three Divine Persons from eternity were to be acknowledged; and that although each Person separately was by Himself God, yet three Gods and Lords were not to be spoken of, but only one.
* The province of north-western Anatolia, now part of Turkey. ** The Council was summoned in 318, but assembled in 325. The Latin text here has 1318, an obvious misprint.