Or HaChaim on Exodus 7:16/אור החיים על שמות ז׳:ט״ז

1 ואמרת אליו ה׳..שלחני אליך, "Say to him: G'd.. has sent me to you, etc." This entire verse appears to be superfluous. Verse 17 would have been quite adequate. Pharaoh did not need to be told that G'd had sent Moses! Perhaps the Torah wanted to tell us that Pharaoh had objected to being met by Moses at a time when he performed his morning ritual. Moses was to explain that he had not intended to invade Pharaoh's privacy but had been commanded by G'd to do so. Moses was to imply that instructions from the Supreme G'd must be carried out immediately.

2G'd may have intended another lesson for Pharaoh, one which is alluded to in Shemot Rabbah 8,1 based on Ezekiel 29,3 where Pharaoh is described as claiming that he had made the river Nile and that he owned it. Since Pharaoh had thus elevated himself to the level of a deity, he had to leave the palace every morning and answer a call of nature where he would not be seen in order that he could maintain the myth of being a god. G'd exploded this myth by sending Moses to him at the time and place Pharaoh had reserved for his very human needs. Moses first told Pharaoh that the G'd of the Hebrews was well aware of his whereabouts and wanted him to know this and embarass him with this knowledge. Pharaoh was now under threat that his myth might be shattered if Moses were to tell his servants of their master's weakness. When G'd added that so far Pharaoh had not listened to him, He wanted Pharaoh to know that though the latter had not specifically refused Moses' latest demand, G'd could read his thoughts.

3The words "the G'd of the Hebrews has sent me to you," may also be a way of telling Pharaoh that the demand to release the Israelites need not be repeated before Moses would strike the river Nile and turn it into blood. The word כה was quite enough to show us that the plague that follows was the result of the demand to let the Israelites go which Pharaoh had thus far ignored. After all, Moses had previously identified himself and Pharaoh had ignored the demand to dismiss the Israelites. If Pharaoh thought that the fact that he had not yet been smitten for his refusal was a sign that G'd's threats were not to be taken seriously, he would find out immediately how wrong he had been.