And these are the generations of Aaron and Moses on the day that God spoke to Moses on Mount Sinai (Numbers 3:1). Anyone with whom the Omnipresent engages to establish a nation or a family tree from him, the Omnipresent would also engage with him to write generations in his regard, as you find twelve instances of generations in the verses. The first: “These are the generations of the heavens and the earth” (Genesis 2:4); “this is the book of the generations of Adam” (Genesis 5:1); “these are the generations of Noah” (Genesis 6:9); “these are the generations of the sons of Noah” (Genesis 10:1): “these are the generations of Shem” (Genesis 11:10); “these are the generations of Teraḥ” (Genesis 11:27); “these are the generations of Ishmael” (Genesis 25:12); “Isaac” (Genesis 25:19); “Esau” (Genesis 36:1); “Jacob” (Genesis 37:2).
These are ten generations with which the Holy One blessed be He engaged to create the world and to establish nations. And there are two people that the Omnipresent wrote their generationst, one for the royal dynasty and one for the priestly dynasty: “These are the generations of Peretz” (Ruth 4:18), to establish the royal dynasty from him, and “these are the generations of Aaron and Moses"(Numbers 3:1), for the priestly dynasty.