1Jude, a servant of Jesus Christ, and brother of James, to those who are called, sanctified by God the Father, and kept for Jesus Christ: 2May mercy, peace, and love be multiplied to you.
3Beloved, while I was very eager to write to you about our common salvation, I was constrained to write to you exhorting you to contend earnestly for the faith which was once for all delivered to the saints. 4For there are certain men who crept in secretly, even those who were long ago written about for this condemnation: ungodly men, turning the grace of our God into indecency, and denying our only Master, God, and Lord, Jesus Christ.
5Now I desire to remind you, though you already know this, that the Lord, having saved a people out of the land of Egypt, afterward destroyed those who didn’t believe. 6Angels who didn’t keep their first domain, but deserted their own dwelling place, he has kept in everlasting bonds under darkness for the judgment of the great day. 7Even as Sodom and Gomorrah and the cities around them, having in the same way as these given themselves over to sexual immorality and gone after strange flesh, are shown as an example, suffering the punishment of eternal fire. 8Yet in the same way, these also in their dreaming defile the flesh, despise authority, and slander celestial beings. 9But Michael, the archangel, when contending with the devil and arguing about the body of Moses, dared not bring against him an abusive condemnation, but said, “May the Lord rebuke you!” 10But these speak evil of whatever things they don’t know. They are destroyed in these things that they understand naturally, like the creatures without reason. 11Woe to them! For they went in the way of Cain, and ran riotously in the error of Balaam for hire, and perished in Korah’s rebellion. 12These are hidden rocky reefs in your love feasts when they feast with you, shepherds who without fear feed themselves; clouds without water, carried along by winds; autumn trees without fruit, twice dead, plucked up by the roots; 13wild waves of the sea, foaming out their own shame; wandering stars, for whom the blackness of darkness has been reserved forever. 14About these also Enoch, the seventh from Adam, prophesied, saying, “Behold, the Lord came with ten thousands of his holy ones, 15to execute judgment on all, and to convict all the ungodly of all their works of ungodliness which they have done in an ungodly way, and of all the hard things which ungodly sinners have spoken against him.” 16These are murmurers and complainers, walking after their lusts—and their mouth speaks proud things—showing respect of persons to gain advantage.
17But you, beloved, remember the words which have been spoken before by the apostles of our Lord Jesus Christ. 18They said to you, “In the last time there will be mockers, walking after their own ungodly lusts.” 19These are those who cause divisions and are sensual, not having the Spirit.
20But you, beloved, keep building up yourselves on your most holy faith, praying in the Holy Spirit. 21Keep yourselves in God’s love, looking for the mercy of our Lord Jesus Christ to eternal life. 22On some have compassion, making a distinction, 23and some save, snatching them out of the fire with fear, hating even the clothing stained by the flesh.
24Now to him who is able to keep them from stumbling, and to present you faultless before the presence of his glory in great joy, 25to God our Savior, who alone is wise, be glory and majesty, dominion and power, both now and forever. Amen.
"The oldest, and likely the most widely held, interpretation is that the “sons of God” are fallen angels (demons). This was the interpretation most favored in ancient Judaism and the early church (cf. 1 Pet. 3:19, 20; 2 Pet. 2:4; Jude 6). The phrase “sons of God” is clearly used elsewhere of angelic hosts in God’s heavenly court (cf. Job 1:6; 2:1; 38:7). Moreover, the narrator seems to contrast “man” and “the daughters of man” with the “sons of God” in Genesis 6:1, 2."
"This position is not without difficulties, however, the most substantial of which is the idea of fallen angels having physical relations with women. Scripture gives instances of angels engaging in human activities such as eating (Gen. 18:1, 2, 8; 19:1, 5), but surely sexual intercourse is a step beyond! Jesus makes a similar point in Matthew 22:30: “For in the resurrection they neither marry nor are given in marriage, but are like angels in heaven.” William F. Cook, Who Are the Sons of God in Genesis 6? Some of these church fathers were Justin Martyr, Eusebius, Clement of Alexandria, Origen, and Commodianus. Douglas et al. 2011, p. 1384
Most early church fathers in the first three centuries believed that the sons of God were angels who had unnatural sex with women and bore children. This perspective changed with St. Augustine of Hippo, who argued in the City of God that the sons of God were descendants of Seth.
The argument that Jesus taught that angels in heaven did not marry has no impact on the Genesis 6 passage since the angels in Gen 6, as accepted by Jude and Peter, were not unfallen angels in heaven but evil angels who were part of the fallen angels, or unfallen angels involved in human activity before the flood, who also fell. The ability to have sex and bear children appears to be a major argument against the "angel" view, but one must remember that angels in Gen 18 came in human form, along with Yahweh, ate food and drank, and had their feet washed. Moreover, in the New Testament, angels always appear in a male human form." See my article, Will We Eat and Drink in the Coming Kingdom of God? An Interpretation with Origen, Cerinthus, the Church Fathers, and the Literal Interpretation of the Scriptures on the Nature of the Millennial Kingdom.
6. And the angels who kept not their first estate but left their own habitation, he hath reserved in everlasting chains under darkness the judgment of the great day.
The strongest text that associates the sons of God in Genesis 6:1-4 is the Book of Enoch (6:11), referenced by the writer Jude in 1:6: "When the son of men had multiplied, in those days, beautiful and comely daughters were born to them. 2/ And the watchers, the sons of heaven, saw them and desired them. And they said to one another, "Come, let us choose for ourselves wives from the daughters of men, and let us beget children for ourselves."[1]
The ancients had many traditions of deities cast out from heaven. See notes on Genesis xi. 8. Jove, deceived by the goddess Ate, is represented by Homer as having cast her forth, forbidding her return to Olympus with an oath.
"From his ambrosial head, where perch'd she sat,
He snatched the fiery goddess of debate,
The dread, the irrevocable oath he swore,
The immortal seats should ne'er behold her more;
And whirl'd her headlong down, for ever driven
From bright Olympus and the starry heaven." Il 1. xix. v. 126
Jove declares that any deity who interferes in the strife between the Greeks and
Trojans—
"Far, oh far, from steep Olympus thrown,
Low in the dark Tartarean gulph shall groan,
With burning chains fixed to the brazen floors,
And lock'd by Hell's inexorable doors.''-Hom. ll, 1. xix v. v.3.
" With enduring chains
He bound Prometheus, train'd in shifting wiles,
With galling shackles fixing him aloft."-Hes. Theog. v. 521.
[1] George W. E. Nickelsburg and James C. VanderKam, 1 Enoch: A New Translation (Minneapolis: Fortress Press), p. 23.