This speaks of Yahweh causing armies to bring down the walls as if he himself were going to bring them down. To "abase" the "wall" is a metonym for humiliating the Moabites by destroying the walls they were proud of. Alternate translation: "He will send an army to humiliate you by bringing down the stronghold of your fortress walls and making them fall" (See: [[rc://en/ta/man/jit/figs-metonymy]])
Here "your" refers to the people of Moab. It can be stated in third person to be consistent with the previous verse. Alternate translation: "their fortress" (See: [[rc://en/ta/man/jit/figs-123person]])