Rev 16:2

2 The first went, and poured out his bowl into the earth, and it became a harmful and evil sore on the men who had the mark of the beast, and who worshiped his image.

those who had the mark of the beast and worshiped his image – the changing of the Sabbath Day and the Trinity doctrine. These are two great blasphemies of the beast that arose in the fourth Century, we discussed in Chapter 13. The sores are the discomfort of those who try to maintain these doctrines. These sores are metaphorically inflicted by the hail and fire of the first trumpet.