Martinus C. de Boer, Paul, Theologian of God’s Apocalypse: Essays on Paul and Apocalyptic (Eugene, OR: Cascade Books, 2020), 22.
The story of [the] angelic fall is found or alluded to in much of the literature (1 En. 6-19; 64:1-2; 69:4-5; 86:1-6; 106:13-17; Jub. 4:15, 22; 5:1-8; 10:4-5; T. Reub. 5:6-7; T. Naph. 3:5; CD 2:17-3:1; 2 Bar. 56:12-15; LAB 34:1; Wis 2:23-24; cf. Jude 6; 2 Peter 2:4). The basic story, one that also lies behind Genesis 6:1-6, is that some of God’s angels descended to the earth and married beautiful women, thereby begetting giants. Though there was a preliminary judgment of the angels themselves in the time of the Flood, the giants they begot left behind a host of demonic spirits who continue to pervert the earth, primarily by leading human beings, even God’s own people, astray into idolatry. Furthermore, it is evident that Satan (Mastema, Belial, the devil) and his angels continue to wreak havoc on the earth.