What does Exodus 9:9 mean?
Moses was instructed to throw handfuls of soot or ashes into the air in front of Pharaoh (Exodus 9:8). As the ashes dissipated, they would become a fine dust bringing "boils" and "sores" on men and animals alike. This sixth plague (Exodus 3:20) would involve debilitating, painful skin conditions. Such problems are noted in the lives of men like Job (Job 2:7–8) and Hezekiah (Isaiah 38:21).The exact nature of these boils is uncertain. Several possibilities have been suggested. On one hand, the Egyptians recently experienced a wave of infesting insects (Exodus 8:17, 24). These can bring disease, including bacteria that cause painful ulcers on the skin. In that case, it would mean God using that mechanism to further punish Pharaoh and the Egyptian slaveholders. On the other hand, the effects seem to happen so rapidly that the men standing in front of Moses are rendered unable to stand (Exodus 9:11). In either case, there is no question that God is the cause of the disaster. Where Egyptian idols such as Sekhmet and Isis were expected to prevent such things, they will fail.
This passage does not explicitly say that the lands and people of Israel would be spared (Exodus 9:4, 26; 10:23). Given the context, however, it seems likely that the Hebrews were not subjected to these boils and sores. God will later include similar troubles as part of Israel's promised punishment for breaking their covenant with the Lord (Deuteronomy 28:27, 35).