What does Obadiah 1:9 mean?

Edom was blessed with riches and excellent terrain. Cliffs and mountains are hard to attack. So, as a wealthy and secure people, the Edomites saw themselves as "mighty." Since their warriors hadn't suffered the kind of defeats Israel had, Edom felt they were a greater military power than they really were. This led to overconfidence, and an assumption of their own wisdom. Like some modern sports teams, Edom seems to have confused "undefeated" with "undefeatable."

The surprise attack which defeated Edom came not long after this prophecy was given. As a result, the warriors and wise men were caught unaware, and obliterated. Verses 8 and 9 not only predict this event, they serve to humiliate Edom. The very strengths the Edomites bragged about will be turned upside down when judgment comes.

"Mount Esau" and "Mount Seir" are references to the nation of Edom. These people were the children of Esau, the brother of Israel's father, Jacob. Edom's cities were in the mountains of Seir, Southeast of Israel. Teman was Esau's grandson, and the capital city of Edom was named after him.