Obadiah, which means "Servant of Yah", made his predictions sometime after the fall of Jerusalem in 586 BC, and before the Nabation conquest of Edom. His book is the shortest book in the Old Testament, consisting of only one chapter with 21 verses. It concerns the destruction of Edom, a nation who participated in the destruction of Jerusalem in 586 BC.
The Edomites were descendants of Esau, while the Israelites were the descendents of Jacob. (Jacob and Esau were brothers). It is for this violence of brother Edom against brother Israel, that Edom is condemned. Rather than help Israel when the nation was being attacked, Edom helped the attackers and took part in the plundering of Israel.
The subject of this little book is that the judgment of God does not overlook the wrongs done by evil men or nations but visits them with retribution.
The Bible's book of Obadiah is the fourth of the twelve minor prophets.