Feast of St Patapius the Righteous of Thebes and the Forefeast of the Conception by St Anna of the Most Holy Theotokos
THE HOLY Catholic and Apostolic Church teaches that the Father exists simultaneously with His only-begotten Son, who is begotten of Him without time or change or passion and in a manner beyond understanding, as only the God of all knows. They exist simultaneously, as does the fire with its light—without the fire being first and the light afterwards, but both simultaneously. And just as the light is ever being begotten of the fire, is always in it, and is in no way separated from it, so also is the Son begotten of the Father without in any way being separated from Him, but always existing in Him. However, the light, which is inseparably begotten of the fire and always remains in it, does not have any individual existence apart from the fire, because it is a natural quality of the fire. On the other hand, the only-begotten Son of God, who was inseparably and indivisibly begotten of the Father and abides in Him always, does have His own individual existence apart from that of the Father.
Now the Word is also called “Brightness” (Heb. 1.3) because He was begotten of the Father without copulation, without passion, without time, without change, and without separation. He is also called “Son” and “Figure of the substance of the Father” (cf. St Gregory Nazianzen, Sermon 30.20) because He is perfect and distinctly subsistent and in all things like the Father except in the Father’s being unbegotten. And He is called “Only-begotten” because He alone was begotten alone of the only Father. For neither is there any other begetting like that of the Son of God, nor is there any other Son of God. Thus, although the Holy Ghost does proceed from the Father, this is not by begetting but by procession. This is another manner of existence and is just as incomprehensible and unknowable as is the begetting of the Son. Hence, the Son has all things whatsoever the Father has, except the Father’s being unbegotten, which does not imply any difference in substance, nor any quality, but, rather, a manner of existence (cf. St Basil, Against Eunomius 4). Thus, in the same way, Adam is unbegotten, because he was formed by God, while Seth is begotten, because he is the son of Adam; Eve, too, was not begotten, because she was produced from the rib of Adam. Yet, they do not differ in nature, because they are all human beings; they only differ in the manner of their existence.
—St John of Damascus, An Exact Exposition of the Orthodox Faith