2 Peter 2:4

For if God spared not the angels that sinned Better, spared not angels, there being no article in the Greek. Here the nature of the sin is not specified. We may think either of a rebellion of angels headed by Satan, such as Milton has represented in Paradise Lost, or of the degradation of their spiritual nature by sensual lust, as in Genesis 6:2. Looking to the more definite language of Jude, 2 Peter 2:6-8, where the guilt of the angels is placed on a level with that of Sodom, it seems probable that the Apostle had the latter in his thoughts.

but cast them down to hell Literally, cast them into Tartarus. The use of a word so closely bound up with the associations of Greek mythology is a phenomenon absolutely unique in the New Testament. A compound form of the same word had been used of Zeus as inflicting punishment on Cronos and the rebel Titans. (Apollodorus, Bibl. 1. 1.) Here it is used of the Almighty as punishing rebellious angels.

delivered them into chains of darkness The MSS. present two readings, one giving a word which literally means a "rope," as in the LXX. of Proverbs 5:22, and may, therefore, rightly be rendered "cords," "bonds," or "chains," so agreeing with the thought of Wis 17:17 ("they were bound with a chainof darkness") and Jude, 2 Peter 2:6, and the other a noun which has probably the meaning of "dens" or "caves." The latter is the best supported, having A, B, C and א in its favour. The two words differ but by a single letter, (1) σειραῖς, and (2) σειροῖς, and as (2) was the less familiar of the two and (1) agreed better with the "everlasting chains" (or "bonds") of Jude 2 Peter 2:6, the change was a natural one for transcribers to make.

to be reserved unto judgment Literally, being reserved. The judgment in Jude, 2 Peter 2:6, is defined as that of the "great day." Here it is left undefined, but it is natural to refer it to the same great day of doom. As far as the text goes, it indicates a difference of some kind between the angels who are thus imprisoned, and the "demons" who torment and harass men on earth, but it would be hazardous to dogmatise with undue definiteness, on the strength of this passing allusion, as to the condition of these inhabitants of the unseen world.