But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name.
For in him dwelleth all the fulness of the Godhead bodily.
In the Creed we confess that Jesus Christ is "the Son of God, the only-begotten, begotten of the Father before all ages. Light of light; true God of true God; begotten, not made; of one essence with the Father". This addresses the reason for calling the council in Nicea in 325. There were men teaching that the Son of God was a created being and not divine by nature. This is contradictory to the Christian faith, so a number bishops were gathered together to make a statement of faith and settle the doctrinal dispute concerning the divinity of the Son.
This foundational truth of the Christian faith can be found witnessed to throughout the New Testament. In the first chapter of the New Testament, we find a reference to Christ as "Emmanuel", or "God with us", and at the annunciation Mary was told "that holy thing which shall be born of thee shall be called the Son of God". Christ's ministry began with His baptism where a voice came from heaven saying "This is my beloved Son, in whom I am well pleased", which was also heard at the Transfiguration. Peter proclaimed Jesus to be "the Son of the Living God" when asked who a Christian disciple is to believe Jesus to be. When Jesus came into contact with those possessed with demons, they would recognize and greet Him as the Son of God. He taught that He "proceeded forth from God" and prayed "And now, O Father, glorify thou me with thine own self with the glory which I had with thee before the world was" before He was to be crucified. We find references throughout the epistles like "Who, being in the form of God, thought it not robbery to be equal with God", "For in him dwelleth all the fulness of the Godhead bodily.", He is referred to as "the image of the invisible God", and that the knowledge of the glory of God is "in the face of Jesus Christ".
We find this teaching echoed in the writings of Christian teachers as they preserved and proclaimed the truth throughout time. These words are attributed to Ignatius of Antioch...
And there is also one Son, God the Word. For “the only-begotten Son,” saith [the Scripture], “who is in the bosom of the Father.” And again, “One Lord Jesus Christ.” And in another place, “What is His name, or what His Son’s name, that we may know?”Justin Martyr says in his Dialogue with Trypho...
“I shall give you another testimony, my friends,” said I, “from the Scriptures, that God begat before all creatures a Beginning, [who was] a certain rational power [proceeding] from Himself, who is called by the Holy Spirit, now the Glory of the Lord, now the Son, again Wisdom, again an Angel, then God, and then Lord and Logos; and on another occasion He calls Himself Captain, when He appeared in human form to Joshua the son of Nave (Nun). For He can be called by all those names, since He ministers to the Father’s will, and since He was begotten of the Father by an act of will; just as we see happening among ourselves: for when we give out some word, we beget the word; yet not by abscission, so as to lessen the word [which remains] in us, when we give it out: and just as we see also happening in the case of a fire, which is not lessened when it has kindled [another], but remains the same; and that which has been kindled by it likewise appears to exist by itself, not diminishing that from which it was kindled.Augustine writes in his On the Holy Trinity
They who have said that our Lord Jesus Christ is not God, or not very God, or not with the Father the One and only God, or not truly immortal because changeable, are proved wrong by the most plain and unanimous voice of divine testimonies; as, for instance, “In the beginning was the Word, and the Word was with God, and the Word was God.” For it is plain that we are to take the Word of God to be the only Son of God, of whom it is afterwards said, “And the Word was made flesh, and dwelt among us,” on account of that birth of His incarnation, which was wrought in time of the Virgin. But herein is declared, not only that He is God, but also that He is of the same substance with the Father...Cyril of Jerusalem writes in his Catechetical Lectures...
But we know Christ to have been begotten not as a word pronounced, but as a Word substantially existing and living; not spoken by the lips, and dispersed, but begotten of the Father eternally and ineffably, in substance. For, In the beginning was the Word, and the Word was with God, and the Word was God... He who hath seen the Son, hath seen the Father: for in all things the Son is like to Him who begat Him; begotten Life of Life and Light of Light, Power of Power, God of God; and the characteristics of the Godhead are unchangeable in the Son; and he who is counted worthy to behold Godhead in the Son, attains to the fruition of the Father.And Patrick writes in his Confession "...and his son Jesus Christ, who manifestly always existed with the Father, before the beginning of time in the spirit with the Father, indescribably begotten before all things...".
We can also find this teaching faithfully echoed in Orthodox catechisms. We find this in the Orthodox Confession of Peter Mohila...
...first, that the Son of God, Jesus Christ, is eternal God, begotten by the Father of his very essence, and is of the same honor and glory with the Father, as he speaks of himself: "Father, glorify me now with yourself, with the glory which I had with you before the world was."... And he is called only-begotten for this reason, that he is the one Son of God according to the divine nature; but certain others are called sons of God by virtue of his freely given grace as all the faithful and the elect of God; this grace of adoption is given to them through Christ, as Sacred Scripture says: "As many as received him, he gave them power to become sons of God."... But he is called "light of light" because he has his total essence from the Father, just as when a light is lit from another light, it receives therefrom the entire substance of light.And we find this taught in the Catechism of St Philaret...
139. Why is Jesus Christ called the Son of God, Only-begotten?
By this is signified that he only is the Son of God begotten of the substance of God the Father; and so is of one substance with the Father; and consequently excels, beyond comparison, all holy angels and holy men, who are called sons of God by grace.
139. Why is Jesus Christ called the Son of God, Only-begotten?
By this is signified that he only is the Son of God begotten of the substance of God the Father; and so is of one substance with the Father; and consequently excels, beyond comparison, all holy angels and holy men, who are called sons of God by grace. John i. 12.
142. Why is it said that he is begotten before all worlds?
That none should think there was ever a time when he was not. In other words, by this is expressed that Jesus Christ is the Son of God from everlasting, even as God the Father is from everlasting.
143. What mean in the Creed the words Light of light?
Under the figure of the visible light they in some manner explain the incomprehensible generation of the Son of God from the Father. When we look at the sun, we see light: from this light is generated the light visible every where beneath; but both the one and the other is one light, indivisible, and of one nature. In like manner, God the Father is the everlasting Light. 1 John i. 5. Of him is begotten the Son of God, who also is the everlasting Light; but God the Father and God the Son are one and the same everlasting Light, indivisible, and of one divine nature.
146. Why is it further added of the Son of God in the Creed that he is begotten, not made?
This was added against Arius, who impiously taught that the Son of God was made.
147. What mean the words, Of one substance with the Father?
They mean that the Son of God is of one and the same divine substance with God the Father.Christ our God, the True Light Who enlightens and sanctifies every person who comes into the world: Seal us with the light of Your Countenance that we may perceive Your Unapproachable Radiance.