For - resumptive in connection with Oba 1:10, wherein Edom was threatened with cutting off for ever.
the day of the Lord - the day in which He will manifest Himself as the Righteous Punisher of the ungodly peoples (Joe 3:14). The “all” shows that the fulfillment is not exhausted in the punishment inflicted on the surrounding nations by the instrumentality of Nebuchadnezzar; but, as in Joe 3:14, and Zec 12:3, that the last judgment to come on the nations confederate against Jerusalem is referred to.
as thou hast done, it shall be done unto thee - the righteous principle of retribution in kind (Lev 24:17; Mat 7:2; compare Jdg 1:6, Jdg 1:7; Jdg 8:19; Est 7:10).
thy reward - the reward of thy deed (compare Isa 3:9-11).