Saviors shall go up to Mount Zion
to rule Mount Esau;
and the kingdom shall be the LORD's.
This is a classic example of what happens when the Holy Spirit speaks through a prophet. Obadiah's short little book is written to chew out the people of Edom for acting traitorously toward Israel and assisting Israel's enemies. In a word, it promises judgement for Edom, which was descended from Esau. But when the judgment came it was not what you'd expect. Edom, the enemy of Israel, was indeed conquered and ruled by a Davidic savior: Jesus. Edomites were, like so many other nations, gathered into the Church, the Davidic kingdom of Christ. Obadiah probably didn't expect that, any more than John the Baptist expected Jesus to do what he did. Prophets merely speak for God, they don't necessarily understand what he tells them to say.