The way the original Greek of this text is put together makes clear that the activities people refuse to give up are specifically twofold: first, the worship of demons and idols (Revelation 9:20b); second, the abuse of people (Revelation 9:21). Both the worship of idols and the abuse of other people are characteristic of the life‑choking fire, smoke, and sulfur that comes with paganism.
20 The rest of mankind, who were not killed by these plagues, did not repent of the works of their hands nor give up worshiping demons and idols of gold and silver and bronze and stone and wood, which cannot see or hear or walk,