For three transgressions of Damascus, even four: This phrase describes ongoing rebellion against the natural order set by God. The Hebrew phrase does not describe an exact number. Instead, it points to a pattern of repeated wrongdoing.
they threshed: Threshing grain was the process of separating the grain heads from their husks. People did this by pulling wooden sledges with sharp edges over the cut grain (Isaiah 41:15; see Micah 4:13). This image helps explain how harsh and violent the actions of the people of Damascus were.