It says and again after that. It happened again after the flood and the book of Jude explains what God did to stop it from happening again.
Are you referring to this passage from Jude where we read men of faith must contend earnestly for the faith because many false believers have crept in among them to destroy the saints (church)? Jude reminds them they once knew this and reminded them again that these deceivers, ungodly men who deny the Lord were already ordained to condemnation.
Jude 1 ¶ Jude, the servant of Jesus Christ, and brother of James, to them that are sanctified by God the Father, and preserved in Jesus Christ,
and called:
Jude 2 Mercy unto you, and peace, and love, be multiplied.
Jude 3 ¶ Beloved, when I gave all diligence to write unto you of the common salvation, it was needful for me to write unto you, and exhort
you that ye should earnestly contend for the faith which was once delivered unto the saints.
Jude 4 For there are certain men crept in unawares, who were before of old ordained to this condemnation, ungodly men, turning the grace of our God into lasciviousness, and denying the only Lord God, and our Lord Jesus Christ.
Jude 5 I will therefore put you in remembrance, though ye once knew this, how that the Lord, having saved the people out of the land of Egypt, afterward destroyed them that believed not.
By way of reminding them Jude speaks of the messengers of God, not angels but humans. These are sons of God of Old not only in the days before the flood, but also those men reserved in everlasting chains under darkness to await the great judgment day. Just as men of Sodom and Gomorrha, who gave them over to fornication also reserved for vengeance of eternal fire. Jude calls these men dreamers who defile the flesh, despise dominion and speak evil against God and His saints.
Jude 6 And the angels [messengers] which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.
Jude 7 Even as Sodom and Gomorrha, and the cities about them in like manner, giving themselves over to fornication, and going after strange flesh, are set forth for an example, suffering the vengeance of eternal fire.
Jude 8 ¶ Likewise also these
filthy dreamers defile the flesh, despise dominion, and speak evil of dignities.
Jude refers them to brute beasts, corrupting themselves, who have gone the way of Cain, and greedily the error of Balaam. But like these men of Old these too will perish from the earth in due season. Jude tells us that Enoch, preached of these men, saying the Lord will come with ten thousand of his saint. They are ungodly men of flesh and blood, not spirits called angels of God. Jude ends this letter reminding the saints to remember the words spoken by the apostles of Christ, who repeatedly warn us to guard the flock of God, watch and pray, and to separate ourselves from those who have not the Spirit of Christ.
Jude 9 Yet Michael the archangel, when contending with the devil he disputed about the body of Moses, durst not bring against him a railing accusation, but said, The Lord rebuke thee.
Jude 10 But these speak evil of those things which they know not: but what they know naturally, as brute beasts, in those things they corrupt themselves.
Jude 11 Woe unto them! for they have gone in the way of Cain, and ran greedily after the error of Balaam for reward, and perished in the gainsaying of Core.
Jude 12 These are spots in your feasts of charity, when they feast with you, feeding themselves without fear: clouds
they are without water, carried about of winds; trees whose fruit withereth, without fruit, twice dead, plucked up by the roots;
Jude 13 Raging waves of the sea, foaming out their own shame; wandering stars, to whom is reserved the blackness of darkness for ever.
Jude 14 (KJV) And Enoch also, the seventh from Adam, prophesied of these, saying, Behold, the Lord cometh with ten thousands of his saints,
Jude 15 ¶ To execute judgment upon all, and to convince all that are ungodly among them of all their ungodly deeds which they have ungodly committed, and of all their hard
speeches which ungodly sinners have spoken against him.
Jude 16 These are murmurers, complainers, walking after their own lusts; and their mouth speaketh great swelling
words, having men's persons in admiration because of advantage.
Jude 17 But, beloved, remember ye the words which were spoken before of the apostles of our Lord Jesus Christ;
Jude 18 How that they told you there should be mockers in the last time, who should walk after their own ungodly lusts.
Jude 19 These be they who separate themselves, sensual, having not the Spirit.
