Charles Ellicott Commentary Amos 1:3

"Thus saith Jehovah: For three transgressions of Damascus, yea, for four, I will not turn away the punishment thereof; because they have threshed Gilead with threshing instruments of iron:" — Amos 1:3 (ASV)

CURSE ON DAMASCUS.

Three transgressions... —This form of transgression, which occurs eight times in the prologue, is not an arithmetical, but a strongly idiomatic phrase, signifying “multiplied or repeated delinquencies” (Henderson).

Turn away... —Rather, will not turn it back—i.e., the severe judgment I have purposed. (Compare to 2 Kings 10:32–33.)