Obadiah 1:11

In the day, he says, in which thou didst stand on the opposite side ”. But the Idumeans might have made this objection, “Why dost thou accuse us for having violently oppressed our brother? for we were not the cause why they were destroyed: they had a quarrel with the Assyrians, we labored to protect our own interest in the midst of these disturbances; we sought peace with the Assyrians, and if necessity so compelled us, that ought not to be ascribed to us as a crime or blame.” In this way the Idumeans might have made a defense: but the Prophet dissipates all such pretenses by saying, In the day in which thou didst stand on the opposite side, in the day in which strangers took away his substance, and aliens entered his gates, and cast lots on Jerusalem — were not thou there? Even thou were as one of them. Now this is emphatically introduced — Even thou or, thou also; (Tu etiam ) for the Prophet exhibits it here as a hateful omen: “It was no wonder that the Assyrians and Chaldeans shed the blood of thy brethren, for they were enemies, they were foreigners, they were a very distant people: but thou, who were of the same blood, thou, whom the bond of religion ought to have restrained, and further, even thou, who oughtest by the very claims of vicinity either to have helped thy brethren, or at least to have condoled with them — yea, thou were so cruel as to have been as one of his enemies: this surely can by no means be endured.”

We now perceive what the Prophet meant by saying, In the day in which thou didst stand on the opposite side: it is then as it were, an explanation of the former sentence, lest the Idumeans should make a false excuse by objecting that they had not been violent against their brethren. It was indeed the worst oppression, when they stood over against them; though they were not armed they yet took pleasure in a spectacle so mournful; besides they not only were idle spectators of the calamity of their brethren but were also as it were a part of their enemies. “Hast thou then not been as one of them?” I shall not proceed farther now.