Commentaries:
Israel's leaders boasted that these nations are no match for the power and wealth of Israel. "They may have had their day," they said, "but Israel will not be troubled by them anymore!" They felt so secure in themselves!
Twice in verse 13, Amos makes a play on words. Because these cities were recent victories of Jeroboam II, Israelites were extolling their military might. In Hebrew, however, Lo Debar means "no thing" or "nothing." They were rejoicing over nothing! Karnaim means "horns," a symbol of strength. To paraphrase, they say, "Have we not overcome strength with greater strength?" God's view, however, is that their strength, in which they boast, is of little consequence. A nation of even greater strength will completely conquer them.
John W. Ritenbaugh
Prepare to Meet Your God! (The Book of Amos) (Part Two)