The chapter begins with a stunning simile: God says Moses will be a god to Pharaoh, and Aaron is his prophet. Moses status is remarkable. It is important to remember that the Pharaoh was thought to be a representative of the god Ra (in a special relationship, like a son) so the confrontation is between YHWH and the gods of Egypt. That Moses would be a 'god' to Pharaoh reminds us of the ancient theological meaning of the events (which would be more important to the ancient). The revelation of YHWH as God to the world is a key component to the entire story. This is a long unfolding theophany! 7:2 serves as a spoiler; Israel will leave the land. Then next verse provides fodder for ongoing debates for thousands of years. What does it mean God "hardened" Pharaoh's heart? We will take a look at that question at length as an independent discussion. For the narrative, the interplay of plague and hardened heart provide that tension which require ongoing plagues. The point, as we have seen, is the revelation of YHWH as (true) God.
The Hebrew word, qasha, is one of three used to describe Pharaoh's heart being hardened (with assorted different nuances: made fierce, made dense, made heavy, reinforce, make strong). Note, the reason given (v5): to increase the signs and let all Egypt know who is God. In stark contrast, Moses and Aaron obey God and do as He told them (no more arguing with God).
Verse six suddenly announces the ages of Moses and his elder brother. This continues the recurring pattern in the Torah of a younger brother usurping the place of honor from an older brother. It is a reminder (more for the ancient reader than us) that God acts outside the expectations of human beings. The ages (40x2 and 40x2 +3) are also symbolic. They mark as turning point in the life of the two heroes.
The Lord tells Moses what Pharaoh will say. It's interesting that Pharaoh's request for a sign is not written. [From a Christian/typological perspective, the demand for a sign echos the same request of Jesus by His adversaries.] Now the staff is called Aaron's. There is, however, a change in the Hebrew. The nahas (snake) of Exodus 4:3 (when Moses threw it down) is now a tannin (serpent, but a sea monster in Genesis 1:21). The implication is that it is no ordinary snake and it portends the final disaster for Egypt (it will swallow bala' the Egyptian snakes; connecting it to Exodus 15:12, the only other time this word appears, when the Egyptians are swallowed by the Sea). There are three categories--wisemen, sorcerers and magicians--who engage in lat (root is either 'secret' or 'wrapped' or 'cast'. The implication is some sort of mysterious trick is used to conjure up the snakes). A second Hebrew word (chazak) is used to describe the hardening of Pharaoh's heart (with a connotation of strengthen, to be heavy). 7:14 kabed (meaning heavy, great, massive, difficult, burdensome) is used to describe Pharaoh's heart. It is applied to the refusal to let the people go. This word is the same root as Moses' heavy tongue and the heavy labor imposed upon the Hebrew slaves, subtle connection.
7:15 the next step happens to the Nile River. Rashi, the great medieval scholar, believes Pharaoh was going to relieve himself. Other theories include rituals or state functions, that he went to bathe, or that he was checking the river level. The location resonates with the plague itself, and also hearkens back to the daughter of Pharaoh who found Moses in the river. The "strong-heart" of Pharaoh is resistant and resilient.The threat is to make the river change (like the rod changed) into blood (blood will loom large in the final plague as well, blood on the doorpost will save the people from death). The result will be the fish die and the river will stink (the Hebrew slaves used the same Hebrew word in 5:21 "You've made our smell stink in Pharaoh's eyes). However, the event itself is revelatory--"by this you'll know I'm God." This is a direct assault on the primary resource for life in Egypt. God (YHWH who is, who was, who will be, who makes things be) is revealing Himself to the world as a creator God (who is concerned with justice for His people).
[Many speculate on the meaning of the plagues--connecting them with various Egyptian gods, for example. In addition, some scholars detect the possibility that there are numerous traditions brought together from different sources and woven together in the current form. In depth analysis of the element of the plagues (cf Everett Fox, Torah, p253) allows for divisions into groups based on themes, verbal content, time of day when threat is made, etc. He sees numerical considerations in play 3+3+3+1=10 (3, 7 and 10 are holy numbers) in some of the divisions. While interesting and important for understanding the Hebrew author, analyzing the twenty different 'words, phrases and motiffs' becomes too technical for my concerns.
The narrative continues with God telling Moses to tell Aaron what to do, and Moses and Aaron do it. Not only the Nile but also the "wood and stone". Most translations add the English word "vessel" assuming it is reference to storage, dishware or utensils, however Fox (295) remarks that "virtually everywhere in the Bible that "wood and stone" occur as a pair in the singular; they refer to idols"--hence, following Cassuto, it may be a subtle reference to Egyptian gods and idols and indicates that YHWH denigrates them! The plague extends throughout the land [making v22 "the magicians of Egypt did thus with their occult-arts" very confusing. What water was left to turn to blood?]. Pharaoh is chazak (means resolute, strong willed, firm) in resisting God, and pays it no mind (the Hebrew words leb gam--literally mean to lay + the inner man/the heart). This is in marked contrast to the people of Egypt. In a sense, the battle is now brought to bear on those who have benefited from the slave labor. The Egyptians are reduced to digging for water along the banks of the river. The period of time, seven days, recalls creation. The Hebrew word, "fill up" recalls that the Hebrew slaves filled up the land.
Next YHWH says to Moses, go to Pharaoh and say to him, "Thus says the YHWH (Lord)" This is classical prophet language. The frogs will be everywhere, ten different recipients are identified (seven places: house, bedroom etc. and three people, "you, your people your servants")