2:4 angels when they sinned. The meaning of this phrase is disputed. Many view this as an allusion to the sin of the “sons of God” in Gen. 6:1–4 (cf. Jude 6). On this reading, Peter may be assuming for illustrative purposes the elaboration of the Gen. 6 narrative in the apocryphal book of 1 Enoch (Jude 14 note). While “sons of God” can refer to angels (e.g., Job 1:6; 2:1), this interpretation is not without difficulties (Gen. 6:2 note). Others speculate that the “angels” are the evil angels who sinned before the Fall of humanity in Gen. 3. Either way, the point is that if God judged evil angels, He will certainly judge ungodly people as well.
cast them into hell. The verb means “to cast into Tartarus.” In Greek mythology Tartarus was the place of punishment for departed spirits. Just as Paul can quote an apt verse from a pagan writer for his own purposes (cf. Acts 17:28; Titus 1:12), so Peter here uses Homeric imagery to convey the idea of a special place of confinement until final judgment.