If not of the essence of God, the Son could not be held to be eternal.  “How utterly absurd,” exclaims Basil, “to deny the glory of God to have had brightness; ἀπαύγασμα.  cf. Heb. i. 13. to deny the wisdom of God to have been ever with God!…The Father is of eternity.  So also is the Son of eternity, united by generation to the unbegotten nature of the Father.  This is not my own statement.  I shall prove it by quoting the words of Scripture.  Let me cite from the Gospel ‘In the beginning was the Word,’ John i. 1. and from the Psalm, other words spoken as in the person of the Father, ‘From the womb before the morning I have begotten them.’ Ps. cx. 3, LXX.   Let us put both together, and say, He was, and He was begotten.…How absurd to seek for something higher in the case of the unoriginate and the unbegotten!  Just as absurd is it to start questions as to time, about priority in the case of Him Who was with the Father from eternity, and between Whom and Him that begat Him there is no interval.” Id. ii. 17.