Make thyself many as the cankerworm - On the locusts, and their operations in their various states, see the notes on Joel 2 (note). The multitudes, successive swarms, and devastation occasioned by locusts, is one of the most expressive similes that could be used to point out the successive armies and all-destroying influences of the enemies of Nineveh. The account of these destroyers from Dr. Shaw, inserted Joel 2, will fully illustrate the verses where allusion is made to locusts.
There - where thou didst fence thyself, and madest such manifold and toilsome preparation,
Shall the fire devour thee. - All is toil within. The fire of God‘s wrath falls and consumes at once. Mankind still, with mire and clay, build themselves Babels. “They go into clay,” and become themselves earthly like the mire they steep themselves in. They make themselves strong, as though they thought “that their houses shall continue forever” Psalm 49:11, and say, “So, take thine ease eat, drink and be merry” Luke 12:19-20. God‘s wrath descends. “Thou fool, this night thy soul shall be required of thee. It shall eat thee up like the canker-worm.” What in thee is strongest, shall be devoured with as much ease as the locust devours the tender grass. The judgments of God, not only overwhelm as a whole, but find cut each tender part, as the locust devours each single blade.
Make thyself many as the cankerworm - As though thou wouldest equal thyself in oppressive number to those instruments of the vengeance of God, gathering from all quarters armies to help thee; yea, though thou make thy whole self one oppressive multitude, yet it shall not avail thee. Nay, He saith, thou hast essayed to do it.