Why does the Creed proclaim that He is the Only Begotten Son of God?

The heavenly Father witnessed of Him during His baptism and transfiguration. Of His baptism, the Gospel of Matthew says, “and behold, the heavens were opened to Him … and

313 St. Cyril of Jerusalem, Catechetical Lectures 10.3 (NPNF II/7:57–58) amended.

suddenly a voice came from heaven, saying, ‘this is My beloved Son , in whom I am well pleased.’” (Matt. 3:16–17). And of His transfiguration on Mount Tabor, it was also said: “While he was still speaking, behold, a bright cloud overshadowed them; and suddenly a voice came out of the cloud, saying, ‘This is My beloved Son, in whom I am well pleased. Hear Him!’” (Matt. 17:5).

When He asked His disciples: “‘But who do you say that I am?’ Simon Peter answered and said, ‘You are the Christ, the Son of the living God.’ Jesus answered and said to him, ‘Blessed are you, Simon Bar-Jonah, for flesh and blood has not revealed this to you, but My Father who is in heaven.’” (Matt. 16:15–17). Christ the Lord distinguished between His eternal sonship to the Father by nature on the one hand, and our being the children of God through grace on the other (Matt. 5:48); for He says, “My Father and your Father” (John 20:17). And after His resurrection and ascension, St. John the Beloved says, “and we beheld His glory, the glory as of the only begotten of the Father, full of grace and truth” (John 1:14).

St. Cyril the Great says, “Yet when they spoke of the Son, in order that they may not seem to attribute an ordinary name to him, one which perhaps could be assigned even to us ourselves, for we are also called sons (Gal. 4:6), they very prudently affix those names … they say that he was begotten not created, knowing him to be in essence untouched by creation by not being created, but rather affirming confidently that he was begotten of the essence of God the Father independently of time and incomprehensibly for ‘in the beginning was the Word’ (John 1:1) … The incorporeal will not beget according to the body, but rather in this way, namely, as light of light … Thus we say the Son is in the Father, and the Father in the Son (John 14:9–10) … Accordingly he is consubstantial with the Father … so that the begetting might be incorporeal and simple and have the concept of being from him and in him and that each subsists in his own person, for the Father is the Father and not the Son, and the Son is the one begotten and not the Father.”³¹⁴