וְאֵ֛לֶּה תֹּלְד֥וֹת עֵשָׂ֖ו אֲבִ֣י אֱד֑וֹם בְּהַ֖ר שֵׂעִֽיר׃
Inilah keturunan Esau, bapak bangsa Edom, di pegunungan Seir.
Shenei Luchot HaBerit
The reason why Joseph has to be dispatched in the future before the arrival of the משיח בן דוד is because he is the natural enemy of Esau inasmuch as he is his exact opposite. Esau is full of the pollutants of the serpent, Joseph, on the other hand, was singularly free of that pollution, as we have explained.