(Exodus 15:15) "Then the chiefs of Edom were confounded": If you say because they (thought) they were coming to inherit their land, is it not written (Devarim 2:5) "… for I will not give you of their (Edom's) land"? What, then, is the intent of "Then the chiefs of Edom were confounded"? Because of worry (over contention.)
Then the Chiefs of Edom Were Confounded
Mekhilta Tractate Shirah 9:15