Obadiah’s (his name means ‘servant of Yahweh’) is the shortest book in the Old Testament, at only 21 verses. He prophesies against Edom, Israel’s long-time enemy (see Numbers 20:14-21, 1 Samuel 14:47, 2 Samuel 8:13-14, 2 Kings 8:20-22). This hostility continued into the exilic and post-exilic period, hence the oracles against them here in Obadiah and elsewhere.
The prophet’s message follows the pattern of the OT oracles: judgment and salvation. Verses 1-9 cover the destruction of proud Edom. Verses 10-14 tell us what Edom was guilty of: being an enemy of God’s people. Yahweh doesn’t take that lightly, and pronounces judgment on all nations guilty of the same charge in verses 15-16.
The end of verse 18 states that there would be no survivors from the house of Esau. This was fulfilled in about 100 B.C. when John Hyrcanus, a Maccabeean, forced the remaining Edomites (then called Idumeans) to become Jews (e.g. the Herods were Idumeans).
Verses 17-21 promise deliverance for God’s people. Yahweh has shown that He’s able to do what He says he will do, as in the paragraph above. Those who have put their faith in Christ can trust Him to bring about His uncontested reign.
Sources: Bible.org, John Woodhouse