The overall theme of the book of Obadiah is judgement that has been brought against the Edomite Nation for the evil they had done to their Israelite brothers and thus God decreed Edom's ultimate destruction. In the text itself, certainly this is a very serious incident that occurs, not to mention with the death of Herod's family line in the New Testament, This prophecy against Edom has been fulfilled.
But does the book have any baring on us today? The answer is yes. God will bring judgement upon those who persecute the Jews as a whole. The Jews in the Old Testament were subject God's judgement because of disobedience and the other nations were used as a means of correction. When the Gentile Nations overstepped the mark and were cruel to them, God punished the nations. Where are the Philistines, Where are Moab and Ammon, Where has Edom gone? All of them have disappeared as a result of what they did and in other texts in the Old Testament were judged by God for their actions.
It is also a sober reminder to us that God's wrath is burning against any nation that violates his decrees and commands, although he will relent if there is repentance towards him. If however a nation turns from good and does evil and don't repent, then those nations are lost.
It is the same principle with any nation, including the Aztecs and the ancient Egyptians. The modern day Egyptians today are Arabs, if not the majority of people living in the Middle East are Arab people, rather than the nations that occupied the territories in the Old Testament.
God is God, he is forever the same, he never changes. If he brought destruction on nations in the Old Testament, he'll do the same thing in the New Testament and in the Modern Era. We need to hold onto this picture of God that he is holy, majestic, and doesn't wink the eye at sin.
Hope this article has been a blessing.