Musar su Salmi 137:7

We find that the שר של מצרים, Egypt's spiritual representative in the Celestial Spheres, was called בכור, i.e. he was the first or senior of the representatives of the seventy Gentile nations. We have explained previously that this spiritual representative of Egypt was described in פרשת מקץ as the מרכבת המשנה, G–d's secondary chariot or carrier. Egypt was second only to the land of Israel in this respect. The land of Israel was G–d's own share in this world. Egypt, however, played the role of first-born amongst the 70 Gentile nations. As a corollary we find that physically speaking, Esau was a first-born, for it was his respective שר who appeared first at the Celestial Court. This שר is a powerful force seeing that his protege became the instrument that destroyed the Holy Temple because of our sins, as mentioned in Psalms 137,7 where the Jewish people are reported as asking G–d to redress that outrage. Alas, this שר is still very powerful. We must view the שר של מצרים as the first of a number of forces who succeeded in dominating Israel in exile. G–d humiliated that force at the time of the Exodus. The שר של עשו, on the other hand, is the very last of such forces. He is so powerful that the present exile is called the גלות אדום. He may therefore be considered the head of the existing שרים. It is this force that Jeremiah refers to in Lamentations 1,5: "Its (Israel's) oppressors have become לראש, a head." Whenever an oppressor of Israel is temporarily successful, he becomes a ראש, head. What all this means is that whereas the שכינה, G–d's Presence, does not depart from Israel, does not ignore what happens to Israel, these happenings are nonetheless delegated by G–d to a שר. When our sages frequently describe the שכינה as being in exile, this is what they mean. When a שר assumes a role as ראש, this means that G–d's Presence has subordinated itself, so to speak. In practice this means that Esau has regained his position as Isaac's first-born and will retain it until the redemption, when G–d will de-throne him. All the above is an "external" view of things.