They shall cut down; better, they cut down. The prophet is describing a picture which passes before his inner eye. Though it cannot be searched; rather, for it cannot be searched out. The subject of the verb is uncertain.
De Dieu's explanation is, "Because the forest is so dense, so intricate, it is necessary to clear a path by cutting down the trees." But this does not seem to suit the context. Surely no other reason was required for the destruction of the "forest" than the will of the wood cutters.
"Searching out" occurs in Job (Job 5:9; Job 9:10; Job 36:26; comp. also 1 Kings 7:47) in connection with numbering, and the second half of the verse expressly describes the foe as innumerable. The singular alternates with the plural, as in Isaiah 5:28, a host being regarded sometimes as a whole, and sometimes as an aggregate of individuals.
Than the grasshoppers; rather, the locust. The name is one of nine which we find given to the various species of locusts in the Old Testament, and means "multitudinous."