Albert Barnes Commentary Obadiah 1:15

"For the day of Jehovah is near upon all the nations: as thou hast done, it shall be done unto thee; thy dealing shall return upon thine own head." — Obadiah 1:15 (ASV)

For the day of the Lord is near upon all the pagan – The prophet once more enforces his warning by preaching judgment to come. “The day of the Lord” was already known (Joel 1:15; Joel 2:1, 31) as a day of judgment upon “all nations,” in which God would “judge all the pagan,” especially for their outrages against His people. Edom might hope to escape if it were threatened alone.

The prophet announces one great law of God’s retribution, one rule of His righteous judgment: As you have done, it shall be done to you. Pagan justice acknowledged this to be just and placed it in the mouth of their ideal of justice. Blessed is he, says the Psalmist (Psalms 137:8), that recompenses to you the deed which you did to us. “Blessed,” because he was the instrument of God.

Having laid down the rule of God’s judgment, the prophet resumes his sentence to Edom and speaks to all through him. In the day of Judah’s calamity, Edom made itself as “one of them.” It, Jacob’s brother, had ranked itself among the enemies of God’s people. Therefore, it too should be swept away in one universal destruction.

It takes its place with them, undistinguished in its doom as in its guilt, or it stands out as their representative, having the greater guilt because it had the greater light. Obadiah, in adopting Joel’s words (Joel 3:7), your reward shall return upon your own head, thereby pronounces upon Edom all those terrible judgments contained in the sentence of retribution as they had been expanded by Joel.