1 But false prophets also arose among the people, just as there will also be false teachers among you, who will secretly introduce destructive heresies, even denying the Master who bought them, bringing swift destruction upon themselves.
2 Many will follow their sensuality, and because of them the way of the truth will be maligned;
3 and in their greed they will exploit you with false words; their judgment from long ago is not idle, and their destruction is not asleep.
4 For if God did not spare angels when they sinned, but cast them into hell and committed them to pits of darkness, reserved for judgment;
5 and did not spare the ancient world, but preserved Noah, a preacher of righteousness, with seven others, when He brought a flood upon the world of the ungodly;
6 and if He condemned the cities of Sodom and Gomorrah to destruction by reducing them to ashes, having made them an example to those who would live ungodly lives thereafter;
7 and if He rescued righteous Lot, oppressed by the sensual conduct of unprincipled men
8 (for by what he saw and heard that righteous man, while living among them, felt his righteous soul tormented day after day by their lawless deeds),
9 then the Lord knows how to rescue the godly from temptation, and to keep the unrighteous under punishment for the day of judgment,
10 and especially those who indulge the flesh in its corrupt desires and despise authority.
Daring, self-willed, they do not tremble when they revile angelic majesties,
6 And angels who did not keep their own domain, but abandoned their proper abode, He has kept in eternal bonds under darkness for the judgment of the great day,
7 just as Sodom and Gomorrah and the cities around them, since they in the same way as these indulged in gross immorality and went after strange flesh, are exhibited as an example in undergoing the punishment of eternal fire.
Strange=> heteros...another of another kind or sort.
a.1. Job 1:6 Now there was a day when the sons of God came to present themselves before the Lord, and Satan also came among them.
a.2. Job 38:7 When the morning stars sang together and all the sons of God sang for joy?
1 Now it came about, when men began to multiply on the face of the land, and daughters were born to them,
2 that the sons of God saw that the daughters of men were beautiful; and they took wives for themselves, whomever they chose.
3 Then the Lord said, "My Spirit shall not strive with man forever, because he also is flesh; never the less his days shall be one hundred and twenty years.
4 The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of men, and they bore children to them. Those are the mighty men who were of old, men of renown.
5 then the Lord saw that the wickedness of man whas great on the earth, and that every intent of the thoughts of his heart was only evil continually.
6 And the Lord was sorry that He made man on earth, and He was grieved in His heart.
7 The Lord said, "I will blot out man whom I have created from the face of the land, from man to animals to creeping things and to birds of the sky, for I am sorry that I have made them."
8 But Noah found favor in the eyes of the Lord.
3.c. I believe it was probably true. He could have spared all the animals, but He chose the ones to send to the ark. Noah didn't go out and capture them.
4.a. 1 Peter 3:18-20
18 For Christ also died for sins once for all, the just for the unjust, in order that He might bring to us God, having been put to death in the flesh, but made alive in the spirit;
19 in which also He went and made proclaimation to the spirits now in prison,
20 who once were disobedient, when the patience of God kept waiting in the days of Noah, during the construction of the ark, in which a few, that is, eight persons, were brought safely through the water.
They were the sons of God
saw that the daughters of men were beautiful
abandoned their proper abode
took wives for themselves
4.b. man and the angels (who fell) have in their thought and hearts, evil.