Exodus 11:7 But against any of the children of Israel shall not a dog move his tongue, against man or beast: that ye may know how that the LORD doth put a difference between the Egyptians and Israel.
While God was at work in Egypt He wanted the people to know that it was He. He wanted them to know that He took care of His people. Pharaoh and Egypt needed to realize that the calamity wasn’t just an act of nature that was happening to both sides. it was God at work proving a point.
Many times things will happen that are just the rain on the just and on the unjust. At other times you will see God clearly doing a work. We must know that He is at work in our lives and in the ministry that He has placed us in!