Since Apollinaris’ doctrine marred the perfection of his humanity, it was condemned at the Council of Constantinople in 381. This same Council asserted the divinity of the Holy Spirit. From that time the Athanasian doctrine of the Trinity has held the orthodox position in Christianity.
The emperor was pleased with the result and sent Arius and his supporters into banishment. Outside of the Holy Scriptures, the Nicene Creed is the most important document the Church holds to establish orthodoxy.
The Festal Letter of Athanasius in 367 contains the names of twenty-six books of the New Testament, the same as now. The establishment of the canon set the foundation upon which the Church was built.
Athanasius (c. 296-373) was a young presbyter in the Alexandrian church during the ecumenical council in Nicea (325).