Ge 36:31 Now these were the kings who reigned in the land of Edom before any king reigned over the children of Israel:

32 Bela the son of Beor reigned in Edom, and the name of his city was Dinhabah.

33 And when Bela died, Jobab the son of Zerah of Bozrah reigned in his place.

34 When Jobab died, Husham of the land of the Temanites reigned in his place.

35 And when Husham died, Hadad the son of Bedad, who attacked Midian in the field of Moab, reigned in his place. And the name of his city was Avith.

36 When Hadad died, Samlah of Masrekah reigned in his place.

37 And when Samlah died, Saul of Rehoboth-by -the-River reigned in his place.

38 When Saul died, Baal-Hanan the son of Achbor reigned in his place.

39 And when Baal-Hanan the son of Achbor died, Hadar reigned in his place; and the name of his city was Pau. His wife's name was Mehetabel, the daughter of Matred, the daughter of Mezahab.

40 And these were the names of the chiefs of Esau, according to their families and their places, by their names: Chief Timnah, Chief Alvah, Chief Jetheth,

41 Chief Aholibamah, Chief Elah, Chief Pinon,

42 Chief Kenaz, Chief Teman, Chief Mibzar,

43 Chief Magdiel, and Chief Iram. These were the chiefs of Edom, according to their dwelling places in the land of their possession. Esau was the father of the Edomites.

It was prophesied in Genesis 17:16 that Sarai, whose name was changed into Sarah (meaning princess of the multitude) that from her would come kings of nations.

Ge 17:15 Then God said to Abraham, "As for Sarai your wife, you shall not call her name Sarai, but Sarah shall be her name.
16 "And I will bless her and also give you a son by her; then I will bless her, and she shall be a mother of nations; kings of peoples shall be from her."

Now, the point of the writer here is to show how God fulfilled His promise to Sarah. She eventually became the mother of the nation Israel and other nations. Here, she is shown as to how she became the mother of nations in Esau's line.

This is to encourage the original Israelite readers again to go and possess the land and dwell in it. For just as God fulfilled His promise to Sarah and Esau, He will also fulfill His promise to them --- they too would become a nation.