Justin Martyr

God, when He had made the whole world, and subjected things earthly to man, and arranged the heavenly elements for the increase of fruits and rotation of the seasons, and appointed this divine law-for these things also He evidently made for man-committed the care of men and of all things under heaven to angels whom He appointed over them. …

The Second Apology, Chapter V ↗

Irenaeus

And for a very long while wickedness extended and spread, and reached and laid hold upon the whole race of mankind, until a very small seed of righteousness remained among them: and illicit unions took place upon the earth, since angels were united with the daughters of the race of mankind; and they bore to them sons who for their exceeding greatness were called giants. …

The Demonstration of the Apostolic Preaching, Sections 18-19 ↗

Julius Africanus

When men multiplied on the earth, the angels of heaven came together with the daughters of men. In some copies I found "the sons of God." What is meant by the Spirit, in my opinion, is that the descendants of Seth are called the sons of God on account of the righteous men and patriarchs who have sprung from him, even down to the Saviour Himself; but that the descendants of Cain are named the seed of men, as having nothing divine in them, on account of the wickedness of their race and the inequality of their nature, being a mixed …

Fragment 2 ↗

Bede

And when men began to multiply on the earth and had daughters, the sons of God saw the daughters of men that they were fair; and they took wives for themselves of all whom they chose. "Men" means the offspring of Cain, who, turned away from the view of divine will, subjected their mind solely to human affairs: "sons of God", however, refers to those who were born from the lineage of Seth, who, following the example of their father's devotion, preserved with an inviolate mind the service they owed to God. …

Commentary on Genesis (Hexaemeron) ↗

John Cassian

As long then as there continued that separation of the lines between them, the seed of Seth, as it sprang from an excellent root, was by reason of its sanctity termed "angels of God," or as some copies have it "sons of God;" and on the contrary the others by reason of their own and their fathers' wickedness and their earthly deeds were termed "children of men." Though then there was up to this time that holy and salutary separation between them, yet after this the sons of Seth who were the sons of God saw the daughters of those who …

Conference 8, CHAPTER XXI ↗