Augustine of Hippo : There is no doubt that this is a mysterious passage. The Scripture wishes to demonstrate the origin of Moses, because his action now required it. His descent began from the firstborn of Jacob, that is, Reuben, and then to Simeon, and then to Levi. It went no further, because Moses was descended from Levi. These men who are mentioned here had already been mentioned among the seventy-five men in whom Israel entered Egypt. For God did not want the first or the second tribe, but the third—that is, the tribe of Levi—to be the priestly tribe. — QUESTIONS ON Exodus 15