Why do I need to know this?
That’s the usual response to reading Genesis 36. It is, after all, just a genealogy and it’s not even about Israel!
But, of course, the chapter is important.
First, you will remember that the promise to Abraham was not only that his descendants would become as numerous as the stars of the sky (the Jews wold be a large nation), but also that Abraham was to become the father of many nations. Proof that came true is found in the listing of Abraham’s children by his second wife, Keturah, the genealogy of Ishmael (Genesis 25) and here with the genealogy of Esau.
Second, the story helps to bring us up-to-date on Esau, how he ended up in Seir and why. The plain point is that God blessed him and Jacob to the extent there was not room enough for them both in the same place.
Third, though Jacob’s sons constituted the people of God, God cared for all of Abraham descendants and wanted Israel to remember they were brethren (see this plainly in Numbers 20:14ff; Deuteronomy 23:7ff; and Obadiah), and act accordingly. When they didn’t, God punished them. Being the chosen people of God is no excuse for not getting along with those who are not. God’s expectation was, and is, that his people will act brotherly toward everyone.