Stop and give it a thought. It's the genealogy of Moses and Aaron - in the middle of Moses' protest that he's not the man to take on Pharaoh...
The story can continue without teh genealogy of our protagonists... but their identity matters to the story as we search for the Christ and his people..
The Israelites are shaped by the prophetic words of their father in Genesis 49. We know from Exodus 2:1 that Moses is a Levite, though we might have expected a Judahite, but this is reinforced by this genealogy.
Exo 6:12 But Moses said to the LORD, "Behold, the people of Israel have not listened to me. How then shall Pharaoh listen to me, for I am of uncircumcised lips?" Exo 6:13 But the LORD spoke to Moses and Aaron and gave them a charge about the people of Israel and about Pharaoh king of Egypt: to bring the people of Israel out of the land of Egypt.
Exo 6:26 These are the Aaron and Moses to whom the LORD said: "Bring out the people of Israel from the land of Egypt by their hosts." Exo 6:27 It was they who spoke to Pharaoh king of Egypt about bringing out the people of Israel from Egypt, this Moses and this Aaron. Exo 6:28 On the day when the LORD spoke to Moses in the land of Egypt, Exo 6:29 the LORD said to Moses, "I am the LORD; tell Pharaoh king of Egypt all that I say to you." Exo 6:30 But Moses said to the LORD, "Behold, I am of uncircumcised lips. How will Pharaoh listen to me?"
The genealogy inserted here of Reuben, Simeon and Levi does nothing directly to move the events on. It is an unexpected genealogy in that it doesn’t reach Judah: Gen 49:3 "Reuben, you are my firstborn, my might, and the firstfruits of my strength, preeminent in dignity and preeminent in power. Gen 49:4 Unstable as water, you shall not have preeminence, because you went up to your father's bed; then you defiled it—he went up to my couch! Gen 49:5 "Simeon and Levi are brothers; weapons of violence are their swords. Gen 49:6 Let my soul come not into their council; O my glory, be not joined to their company. For in their anger they killed men, and in their willfulness they hamstrung oxen.
The genealogy doesn't focus on Reuben and it doesn't get to royal Judah... it tells us about sword-wielding Levi. A good man to send into battle with Pharaoh as the LORD fights for his people.
The genealogy does not change Moses’ confession “How then shall Pharaoh listen to me, for I am of uncircumcised lips.” (6:12, 6:30). Yet, in 7:1, Aaron (the firstborn, 7:7) will speak for Moses as Moses speaks for the LORD to confront Pharaoh. Their words will be their sword as the LORD fights for his people. As in Genesis the grace of God comes to the unexpected one. Identifying the key players in the narrative of the LORD’s Son from slavery under the tyrant of Egypt interprets the story. The Levites fight for the LORD against Pharaoh, and they'll fight for the people before the LORD as priests. Though the Christ will finally come from Judah the Levities will play a vital role.
The genealogy doesn’t merely identify Moses and Aaron as Levites, but looks beyond them to Nadab and Abihu the tragic heirs of Aaron, and to the glorious Phineas son of Eleazar (not to be confused with the later Levite, Phinehas son of Eli) who will take up the fight for the LORD.
Exodus doesn’t just record the events as they happened but provides a later theological analysis. Moses and his prophet Aaron will be the human saviours of the people, as the LORD himself leads them out, Phinehas will take the stage similarly at the close of the book. They represent the people and the LORD as he contends for their freedom. They can speak because they are his people not merely any people.
When Phinehas returns to the narrative it will be: "Phinehas the son of Eleazar, son of Aaron the priest, has turned back my wrath from the people of Israel, in that he was jealous with my jealousy among them, so that I did not consume the people of Israel in my jealousy. Therefore say, 'Behold, I give to him my covenant of peace, and it shall be to him and to his descendants after him the covenant of a perpetual priesthood, because he was jealous for his God and made atonement for the people of Israel.'" (Numbers 25:11-13).
Here is a man after the heart of the LORD who is jealous for his captive son (Exodus 4:23), who proclaims his jealousy in Exodus 20:5 and Exodus 34:14. Here is a true Israelite, an heir to the salvation that the LORD accomplishes for his people when he brings them out of Egypt. The narrative of Exodus 1-5 doesn’t explain why we need to know about Phinehas, Nadab or Abihu, but by the completion of this three volume book they will have played a significant role. The jealousy of the LORD and the intention of his people to share his jealousy is highlighted by the genealogy that leads to the wrath-averting Phinehas (Numbers 25:11) paired with the account of his role in the narrative, the genealogy also serves to highlight the failure of Nadab and Abihu (Leviticus 10:1).
If the narrative is intended to tell the story of a people rescued to obey laws then it is hard to make sense of the extensive non-narrative material about the Tabernacle, High Priest and Sacrifices. However if the narrative can be understood to be one of a priesthood then the narrative makes sense of this material.
The rescue that brings them to the LORD (chapter 19) is for the purpose of their priesthood, as a people with whom the LORD is present (33:15). Whilst there are commands for the people to keep as part of their covenant with the LORD these seem to emphasise their LORD-liness rather than being arbitrary regulations. The main legal material in Exodus 20-23 is concerned with the poor, foreign, orphan and widow, reflecting the heart of the LORD who rescued his people from their oppressive slavery in a foreign land. They are priests to represent the LORD with whom they dwell, whose favour they undeservedly know, to the nations.