C. F. Keil and Franz Delitzsch on Isaiah 14:31

Isa 14:31

The massah consists of two strophes. The first threatens judgment from Judah, and the second - of seven lines - threatens judgment from Asshur. “Howl, O gate! cry, O city! O Philistia, thou must melt entirely away; for from the north cometh smoke, and there is no isolated one among his hosts.” שׁער, which is a masculine everywhere else, is construed here as a feminine, possibly in order that the two imperfects may harmonize; for there is nothing to recommend Luzzatto’s suggestion, that שׁער should be taken as an accusative. The strong gates of the Philistian cities (Ashdod and Gaza), of world-wide renown, and the cities themselves, shall lift up a cry of anguish; and Philistia, which has hitherto been full of joy, shall melt away in the heat of alarm (Isa 13:7, nâmōg, inf. abs. niph.; on the form itself, compare Isa 59:13): for from the north there comes a singing and burning fire, which proclaims its coming afar off by the smoke which it produces; in other words, an all-destroying army, out of whose ranks not one falls away from weariness or self-will (cf., Isa 5:27), that is to say, an army without a gap, animated throughout with one common desire. (מועד, after the form מושב, the mass of people assembled at an appointed place, or mō'ed, Jos 8:14; 1Sa 20:35, and for an appointed end.)