Obadiah 1:12-14 — But thou shouldest not have looked on the day of thy brother in the day that he became a stranger; neither shouldest thou have rejoiced over the children of Judah in the day of their destruction; neither shouldest thou have spoken proudly in the day of distress. Thou shouldest not have entered into the gate of my people in the day of their calamity; yea, thou shouldest not have looked on their affliction in the day of their calamity, nor have laid hands on their substance in the day of their calamity; neither shouldest thou have stood in the crossway, to cut off those of his that did escape; neither shouldest thou have delivered up those of his that did remain in the day of distress.

There are some vices I hate, and some virtues I cherish. Loyalty is very high on my list of virtues. Stand by your friends. Don’t turn you back on your brothers. Simple rules to live by!
The Edomites forgot the rules. They were the descendants of Esau, Jacob’s brother. The brothers had maintained an uneasy relationship. The tribes they founded were mostly separate, but there were “meetings”… Starting with Edom’s refusal to allow Israel passage as they traveled from Egypt to Canaan there were numerous bloody confrontations. Obadiah declares, however, that Edom has gone too far when Israel was invaded.
There are four possible candidates for the invasion that Obadiah speaks of. It is not certain, but scholars generally plump for the invasion by Nebuchadnezzar. Whichever it was, it is certain that at that devastating moment the Edomites turned on their “brothers” to exact a devastating revenge for centuries of grievances. And the Lord would not allow them to go unpunished.
Yesterday, I wrote of the Day of the Lord as a day when the Israelites would be punished for their breach of covenant. James E. Smith makes it clear that Edom’s condemnation has the same roots:

Edom would be put to shame “because of violence to your brother.” The term “brother” was part of the vocabulary of covenant formulation. Two nations with a treaty between them were called brother nations. Thus the crime here charged against Edom is that the terms of the covenant with Jacob, i.e., Israel, had not been observed. In fact, the “brother” Jacob had been treated with “violence,” i.e., wrongful,hurtful action, especially cruelty and oppression.

When Israel was invaded, Edom started as an unhelpful bystander, moved on to be a gloating observer, progressed to being a looter and ended as a hunter and betrayer of the fugitive Israelites. The punishment was to be complete, “For thy violence against thy brother Jacob shame shall cover thee, and thou shalt be cut off for ever.” Obadiah 1:10)
Loyalty is an important virtue. Betraying a brother is not acceptable. My prayer is that we never forget it — personally or nationally!