Charles Ellicott Commentary Amos 1:9

"Thus saith Jehovah: For three transgressions of Tyre, yea, for four, I will not turn away the punishment thereof; because they delivered up the whole people to Edom, and remembered not the brotherly covenant:" — Amos 1:9 (ASV)

CURSE ON TYRUS.

The brotherly covenant. —The “covenant of brethren ” (margin) was the league made between Hiram and David, and afterwards between Hiram and Solomon (2 Samuel 5:11; 1 Kings 5:1; 1 Kings 5:12). This ancient covenant was forgotten in Phoenicia's mercantile greed, and Tyre was tempted to sell Hebrew captives to Greeks and Idumeans. (Ezekiel 26:0, and the special excursus in the Speaker’s Commentary.)