What does Obadiah 1:12 mean?

Verses 12, 13, and 14 continue to accuse Edom, with an interesting twist. The verses say, "Do not," but refer to things which the Edomites have already done. This is an ancient literary technique, as if the author is calling out to the people of the past, saying, "Stop!" This technique can be seen in other Old Testament passages, such as Hosea 9:1. The purpose here is to list the sins of Edom, particularly those against the nation of Israel.

Verse 12 refers to Edom's failure to help Israel when they were attacked by Babylon. In fact, rather than help, the Edomites stood by and laughed while Israel was being invaded. Worse, they helped the Babylonians capture fleeing Jews (Obadiah 1:14), which was probably done with quite a bit of spiteful talk. As it turns out, Edom was actually laughing at a shadow of their own fate. Before long, Edom would be routed and ruined by an invading foreign army.

Edom should have acted as a "brother" nation to Israel, since their ancestors were brothers: Esau and Jacob. Instead, as they had for centuries, the Edomites acted hatefully and cruelly towards the Israelites.