Do you make him leap like a locust, striking terror with his proud snorting?
God, having displayed his own power in those creatures that are strong and despise man, here shows it in one scarcely inferior to any of them in strength, and yet very tame and serviceable to man, and that is the horse, especially the horse that is prepared against the day of battle and is serviceable to man at a time when he has more than ordinary occasion for his service.
Commenting on Job 39:19-25
Canst thou make him afraid as a grasshopper?.... Which is frightened at every noise, and at any approach of men; but not so the horse; or canst thou move him, or cause him to skip and jump, or rather leap like a grasshopper? that is, hast thou given, or canst thou give him the faculty of leaping over hedges and ditches, for which the horse is famous?
make . . . afraid--rather, "canst thou (as I do) make him spring as the locust?" So in Joe 2:4, the comparison is between locusts and war-horses. The heads of the two are so similar that the Italians call the locusts cavaletta, "little horse." nostrils--snorting furiously.