Rev 9:20-21 And the rest of the men which were not killed by these plagues yet repented not of the works of their hands, that they should not worship devils, and idols of gold, and silver, and brass, and stone, and of wood: which neither can see, nor hear, nor walk: 21 neither repented they of their murders, nor of their sorceries, nor of their fornication, nor of their thefts.
As the torment of the hordes of devils begins (9:13-19), the lost will have opportunity to fall on their knees and to beg God for relief and salvation. But even with a third of mankind slain before their eyes (v. 15), they will harden their hearts, refusing to repent of their sins. They will refuse to stop worshiping devils and idols (v. 20), and they will not repent of their murders, acts of sorcery, immorality, and thievery (v. 21). (All references from Revelation)