Moses did not himself set out to battle against this dangerous foe of Israel, but he sent his servant Joshua, and for good reasons. Moses knew that only a descendant of Rachel, like the Ephraimite Joshua, could conquer the descendant of Esau. All the sons of Jacob had taken part in the unbrotherly act of selling Joseph as a slave, hence none of their descendants might stand up in battle against the descendant of Esau; for they who had themselves acted unnaturally to a brother, could hardly hope for God's assistance in a struggle with the unbrotherly Edomites.
Only the descendants of Joseph, the man who had been generous and good to his brothers, might hope that God would grant them aid against the unbrotherly descendants of Esau. In many other respects, too, Joseph was the opposite of Esau, and his services stood his descendants in good stead in their battles against the descendants of Esau. Esau was the firstborn of his father, but through his evil deeds he lost his birthright; Joseph, on the other hand, was the youngest of his father's sons, and through his good deeds was he found worthy of enjoying the rights of a firstborn son.
Joseph had faith in the resurrection, while Esau denied it; hence God said, "Joseph, the devout, shall be the one to visit merited punishment on Esau, the unbelieving." Joseph associated with two wicked men, Potiphar and Pharaoh, yet he did not follow their example; Esau associated with two pious men, his father and his brother, yet he did not follow their example. "Hence," said God, "Joseph, who did not follow example of wicked men, shall visit punishment upon him who did not follow the example of pious men."
Esau soiled his life with lewdness and murder; Joseph was chaste and shunned bloodshed, hence God delivered Esau's descendants into the hands of Joseph's descendants. And, as in the course of history only the descendants of Joseph were victorious over the descendants of Esau, so will it be in the future, at the final reckoning between the angel of Esau and the angels of the Jews. The angel of Reuben will be rebuffed by the angel of Esau with these words, "you represent on who had illegal relations with his father's wife"; the angels of Simeon and Levi will have the listen to this reproof, "You represent people who slew the inhabitants of Shechem"; the angel of Judah will be repulsed with the words, "Judah had illicit relations with his daughter-in-law."
And the angels of the other tribes will be repulsed by Esau's angel, when he points out to them that they all took part in selling Joseph. The only one whom he will not be able to repulse will be Joseph's angel, to whom he will be delivered and by whom he will be destroyed; Joseph will b the flame and Esau the straw burned in the flame.