(Verse 10, 11.) Because of the killing and (the Vulgate adds 'because of') the wickedness against your brother Jacob, shame shall cover you, and you shall perish forever. On the day when you stood against him, when strangers captured his army and foreigners entered his gates, and they cast lots for Jerusalem: you were also like one of them. LXX: Because of the killing and wickedness against your brother Jacob, shame shall cover you, and you shall be taken away forever. From the day that you stood against him, when foreigners captured his strength and strangers entered his gates, they cast lots over Jerusalem, and you were also like one of them. Therefore, a man from the mountain of Esau will perish, and wisdom will be destroyed from Edom, and understanding from the mountain of Esau, because you have killed your brother and acted unjustly against Jacob, when the Chaldeans and Babylonians laid waste to Jerusalem, besieged the city, entered its gates, and cast lots for its treasures. You were their ally and counted among the enemies. Otherwise: you, bloody, earthly, ruthless Edom, will suffer all the things that have been written above, because you have killed your brother Jacob, speaking false and deadly doctrine and speaking impiety against the Lord. We read in Solomon: There are those who speak and kill with the sword (Prov. 25:18). And in another place: The venom of asps is under their lips (Ps. 140:4). And, Their tongue is a sharp sword (Ps. 56:5). Therefore, shame will cover you, and you will say: Shame has covered my face (Ps. 69:8), and you will perish, not for a short time, but forever. For you struck your brother with an eternal wound. But this will also be the cause of torment: for when foreigners were devastating the army of Jacob and entering through its gates into the formerly peaceful Jerusalem, and casting lots to divide its spoils among themselves, you were one of the enemies. We read, we see, and we daily experience that when persecution arises against the Church, the persecutors of Jews and heretics become much worse towards Christians than towards pagans. We can bring foreign ingredients through the gates of Jerusalem, that is, speak evil thoughts, and through the gates of Jerusalem, that is, the soul at rest and seeing God, interpret the five senses through which the enemies enter and divide Jerusalem. If we see a woman to lust after her (Matt. 5), death has entered through our windows (Jer. 9): if we receive lies and the judgement of blood through our ears, the enemy has entered through another gate. Also, the sense of smell, taste, and touch, if it has been captivated by various odors, sweet food, or delicate embraces, enter through other gateways, and divide the spoils of miserable Jerusalem. Therefore, at that time when someone falls from the Church due to the onslaught of persecution and deadly pleasures, we see heretics rejoicing, Jews being glad, and them being counted among the persecutors and included in the number of the Gentiles.
Source: Commentary on Obadiah