In Parshas VaEira, Hashem commanded Moshe to first warn Pharaoh about the impending plague. Moshe told Pharaoh that if he refused to free the Jews to serve Hashem, “so said Hashem, ‘In this you shall know that I am Hashem.’ Behold I am going to strike with the staff that is in my hand upon the water that is in the river, and it shall turn to blood.” After warning Pharaoh, Moshe is then commanded, “Tell Aharon, ‘Take your staff and stretch out your hand over the waters of Egypt…’” Why does Hashem specify that Aharon be the one to initiate the plague? In addition, this pattern is repeated with the next two plagues – Frogs and Lice.