2Peter 2:4-8 For if God spared not the angels that sinned, but cast them down to hell, and delivered them into chains of darkness, to be reserved unto judgment; And spared not the old world, but saved Noah the eighth person, a preacher of righteousness, bringing in the flood upon the world of the ungodly; And turning the cities of Sodom and Gomorrha into ashes condemned them with an overthrow, making them an ensample unto those that after should live ungodly; And delivered just Lot, vexed with the filthy conversation of the wicked: (For that righteous man dwelling among them, in seeing and hearing, vexed his righteous soul from day to day with their unlawful deeds)
‘For if God spared not the angels …’ over one-third of God’s holy angels rebelled with Lucifer (Rev. 12:3, 7-12) and became destined to hell with satan (Matt. 25:41; Isa. 24:21). Many of these committed the additional sin of fornication and are now in hell (2Pet. 2:4; Jude 1:6-7). Angels are sons of God (Gen. 6:1-4; Job 1:6; 2:1; 38:4-7) and yet those who sin are to be punished forever in hell, so sonship is no unforfeitable guarantee of heaven. Three examples of judgment are given:  The fallen angels (2Pet. 2:4). They rebelled with Lucifer when he ruled the earth and when he invaded heaven to dethrone God in the pre-Adamite period (Gen. 1:1-2; Isa. 14:12-14; Ezek. 28:11-17; Jer. 4:23-26; Luke 10:18; 2Pet. 3:5-8).  The ante-deluvians [pre-flood humans] (2:5; Genesis 6-8);  and Sodom and Gomorrah (2:6; Gen. 19:1-38).
‘Sinned’ it does not say here what sin they committed causing them to be confined to hell, but Jude 1:6-7 and Genesis 6:1-4 tell us that they committed fornication, living with the daughters of men contrary to their own nature and produced races of giants on earth which caused a lot of human destruction (Gen. 6:4; Num. 13:33; Deut. 1:28; 2:10-11, 21; 9:2; Josh. 11:21-22; 14:12-14). These angels committed sin beyond that of falling with Lucifer, and they are now confined to hell for that sin. If all the fallen angels had committed such sin they all would now be bound in hell and none loose with the devil to fight against God in the middle of Daniel’s 70th week, 3 1/2 years before the second coming of Christ (Rev. 12:7-17). It would not be just to bind some and not all if the same sin was committed by all. Thus it is clear that there are two classes of fallen angels – those now bound and those now loose with satan.
‘Hell’ [Greek: tartaroo] from tartaros (Latin, tartarus), a dark abyss; a place of punishment. Eight facts about Tartarus: It is a prison for angels and is located under the earth (2:4); it is a place of confinement for angels until the judgment (2:4; Rev. 20:11-15; Jude 1:6); A place visited by Christ when He went to hell (Ps. 16:10; 1Pet. 3:19); It is a place of darkness, eternal fire and vengeance (Jude 1:6-7). The word is used only here but in Greek writings tartarus was held to be a place in the earth lower than hades were the Titans, the primeval deities or the giants who were supposed to be the first children of the earth and even older than the Greek gods, was cast when they lost their war with Zeus.
‘Chains’ [Greek: seira] a cord; rope; chain. It could mean literal chains, for the Greek in Jude 1:6 are desmos which is a band; fetter; halter; imprisonment. Angels can be bound by literal chains and confined to prisons as we see from Revelation 9:1-2, 14; 20:1-3, 7, 10.
‘Of darkness’ Jude 1:6 reads under darkness. The Greek word zophos is used here. It is literal, not spiritual.
‘Spared not the old world, but saved Noah the eighth person, a preacher of righteousness, bringing in the flood upon the world of the ungodly’ we read this history in Genesis 6:1-8:22. ‘Turning the cities of Sodom and Gomorrha into ashes’ See Genesis 19:1-38 for this part of history.
‘Those that after should live ungodly’ Peter refers to God’s judgment when He did not spare the angels, the ante-deluvians, and the cities of Sodom and Gomorrah, and that He will not spare any man who lives ungodly, including the backslider (2:9-22).
‘Filthy’ [Greek: aselgeia] licentiousness and lustfulness. Lasciviousness is the promoting or partaking of that which tends to produce lewd emotions, anything tending to foster sexual sin and lust. That is why many worldly pleasures have to be avoided by Christians – so that lasciviousness may not be committed.
‘Conversation’ [Greek: anastrophe] conduct, behaviour or manner of life; the whole conduct of life in domestic and public relations. Here it refers to sodomy.