16:8 The fourth trumpet judgment darkened the sun (8:12), but this judgment increased the sun's intensity. There is a definite article before "men"in the Greek text. The men in view are evidently the people who have the mark of the beast and who worship him (v. 2). The faithful will apparently escape this judgment. Similarly the Israelites escaped some of the plagues on Egypt.
16:9 Evidently climatic changes will take place resulting in the sun's heat becoming much hotter than normal (cf. Deut. 32:24; Isa. 24:6; 42:25; Mal. 4:1; perhaps the destruction of the ozone layer?). Nevertheless instead of repenting the beast-worshippers curse God (cf. vv. 11, 21). They recognize His sovereignty, but they refuse to honor Him as sovereign (cf. Rom. 1:28; 2:24; 1 Tim. 6:1; James 2:7). Deserved judgment hardens the callous heart even more, as it did Pharaoh.515
"This is the only chapter in the visional portion of the book that speaks of widespread human blasphemy, the other references being to blasphemy from the beast (13:1, 5-6; 17:3). These men have now taken on the character of the god whom they serve . . . They blame God for the first four plagues, rather than blaming their own sinfulness."516
Previously some people repented because of the earthquake in Jerusalem (11:13), but now none do. Giving God glory is the result of repentance.