ב''ה
The individuals who were major players in the stories recounted in the Book of Genesis are not just isolated persons whose influence ended with their deaths. They represent fundamental spiritual thrusts that continued throughout history in the nations they fathered. Almost all of the ancient Biblical nations have become intermingled or seem to have been replaced with more recent peoples. But their spiritual “personalities” continue to be associated with particular nations or groups of nations, or with certain philosophies and approaches that are most popular with certain nations or groups of people.
Esau represents one of the major socio-political thrusts in the spiritual development of world history. This destiny was revealed even before he was born, in Shem’s prophecy to Esau’s mother Rebekah (Genesis 25:23) while she was pregnant with him and Jacob. Shem prophesied to her: “And the L-rd said to her, ‘Two NATIONS are in your womb, and two PEOPLES shall be separated from your insides; and one PEOPLE shall be stronger than the other PEOPLE, and the elder shall serve the younger.’ ”
The alternate name that was given to Esau was Edom (Gen. 25:30), and that became the name of the nation that descended from him. Therefore, since G-d assigns a “prince” (“sar” in Hebrew) angel over each nation, the “sar” angel of the nation of Edom was assigned from the outset to Esau himself. This was the angel that wrestled with Jacob in Gen. 32.25-30. (Note that some other prince/sar angels are mentioned prominently in Daniel ch. 10.)
Esau received a blessing from his father Isaac (Gen. 27:39-40), after Jacob had gone to their father first and secured the blessing for the first-born (Gen. 27:29). Isaac blessed Esau that “of the fatness of the earth shall be your dwelling,” and “by your sword you shall live.” The Midrash identifies this as Rome and southern Italy. In the Torah’s listing of the nations that came from Esau, the second to the last in the list is named “Magdiel” (Gen. 36:43). “Magdiel” means “made great by G-d.” The Midrash identifies this as the Roman Empire, with its capital in Rome.
This is why the angel of Esau/Edom came to be the angel of the Roman empire. It is well known (and this can be found for example in the historical writings of Josephus) that the Romans considered themselves to be the contemporary spiritual power of Esau/Edom.