Lactantius — Divine Institutes 4.13

Therefore the Most High God , and Parent of all, when He had purposed to transfer His religion, sent from heaven a teacher of righteousness, that in Him or through Him He might give a new law to new worshippers; not as He had before done, by the instrumentality of man. Nevertheless it was His pleasure that He should be born as a man , that in all things He might be like His supreme Father. For God the Father Himself, who is the origin and source of all things, inasmuch as He is without parents , is most truly named by Trismegistus fatherless and motherless, because He was born from no one. For which reason it was befitting that the Son also should be twice born, that He also might become fatherless and motherless.

For in His first nativity, which was spiritual, He was motherless, because He was begotten by God the Father alone, without the office of a mother. But in His second, which was in the flesh, He was born of a virgin's womb without the office of a father, that, bearing a middle substance between God and man , He might be able, as it were, to take by the hand this frail and weak nature of ours, and raise it to immortality . He became both the Son of God through the Spirit , and the Son of man through the flesh — that is, both God and man . The power of God was displayed in Him, from the works which He performed; the frailty of the man, from the passion which He endured: on what account He undertook it I will mention a little later.

In the meantime, we learn from the predictions of the prophets that He was both God and man — composed of both natures. Isaiah testifies that He was God in these words: Isaiah 45:14-16 Egypt is wearied, and the merchandise of Ethiopia , and the Sabæans, men of stature, shall come over unto You, and shall be Your servants: and they shall walk behind You; in chains they shall fall down unto You, and shall make supplication unto You, Since God is in You, and there is no other God besides You. For You are God , and we knew You not, the God of Israel , the Saviour. They shall all be confounded and ashamed who oppose You, and shall fall into confusion. In like manner the prophet Jeremiah thus speaks: This is our God , and there shall none other be compared unto Him.

He has found out all the way of knowledge , and has given it unto Jacob His servant, and to Israel His beloved. Afterward He was seen upon earth, and dwelt among men . David also, in the forty-fourth Psalm: Your throne, O God , is for ever and ever; a sceptre of righteousness is the sceptre of Your kingdom. You have loved righteousness, and hated wickedness ; therefore God , Your God , has anointed You with the oil of gladness . By which word he also shows His name, since (as I have shown above) He was called Christ from His anointing. Then, that He was also man, Jeremiah teaches, saying: And He is a man , and who has known Him? Also Isaiah: And God shall send to them a man , who shall save them, shall save them by judging.