The plural indicates that the resistance is not simply to the single plague of “fierce heat.” These angels did not delay pouring out their bowls until the effects of the previous bowl had passed. Instead, the picture is of one plague on top of the other, with a cumulative effect. Recall that the commands in Revelation 16:1 to “go” and to “pour” were written in a form that implies continuous action or repetition. Further, these first four plagues are all of one piece in the sense that they all touch man’s God-given natural habitat. The refusal to repent and to glorify God describes mankind’s reaction to the combined result of the plagues thus far.
9 They were scorched by the fierce heat, and they cursed the name of God who had power over these plagues. They did not repent and give him glory.