For if God did not spare angels when they sinned, but cast them into hell and committed them to chains of gloomy darkness to be kept until the judgment; if he did not spare the ancient world, but preserved Noah, a herald of righteousness, with seven others, when he brought a flood upon the world of the ungodly; if by turning the cities of Sodom and Gomorrah to ashes he condemned them to extinction, making them an example of what is going to happen to the ungodly; and if he rescued righteous Lot, greatly distressed by the sensual conduct of the wicked (for as that righteous man lived among them day after day, he was tormenting his righteous soul over their lawless deeds that he saw and heard); then the Lord knows how to rescue the godly from trials, and to keep the unrighteous under punishment until the day of judgment,
2 Peter 2:4-9
It is not certain what the phrase 'the angels that sinned' refers to (4). Two interpretations are possible: first, that it refers to a revolt of angelic beings prior to the history of man, headed by Lucifer, son of the morning (see Isaiah 14:12ff) thus constituting the world of evil spirits now arrayed against the purposes of God. The second suggestion is that it refers to the passage in Genesis 6:1, 2 which has been interpreted as indicating an unhallowed and illicit union between angelic beings and the daughters of men.
'Noah the eighth person' (5) is a literal translation of the idiomatic phrase which means 'Noah and seven others' (see 1 Peter 3:20). Peter calls him a preacher of righteousness and if we take this along with the reference in the first epistle (3:20) to the longsuffering of God we have a remarkable picture of evangelistic activity in that ancient time.
Lot (7, 8) makes a poor showing in the Old Testament record, living on a far lower level than the saintly Abraham, but he was within the Covenant and as such was preserved. We should learn from this that there is an infinite qualitative distinction between even bad believers and the best of unbelievers. This is not to excuse careless living in believers, nor does the Bible ever do so. Such, as Paul makes clear in 1 Corinthians 3:15, shall suffer loss, and be saved, yet so as by fire. But they shall be saved, whereas unbelievers will be lost, eternally.