And they had breastplates, as it were breastplates of iron - Hard, horny, impenetrable, as if they were made of iron. The locust has a firm and hard cuticle on the forepart of the breast, which serves for a shield or defense while it moves in the thorny and furzy vegetation. On those which John saw this was especially hard and horny, and would thus be well adapted to be an emblem of the breastplates of iron commonly worn by ancient warriors. The meaning is, that the warriors referred to would be well clad with defensive armor.
And the sound of their wings was as the sound of chariots of many horses running to battle - The noise made by locusts is often spoken of by travelers, and the comparison of that noise with that of chariots rushing to battle, is not only appropriate, but also indicates clearly what was symbolized. It was an army that was symbolized, and everything about them served to represent hosts of men well armed, rushing to conflict. The same thing here referred to is noticed by Joel Joel 2:4-5, Joel 2:7;
“The appearance of them is as the appearance of horses;
And as horsemen so shall they run.
Like the noise of chariots on the tops of mountains, shall they leap;
Like the noise of a flame of fire that devoureth the stubble;
As a strong people set in battle array.
They shall run like mighty men;
They shall climb the wall like men of war;
And they shall march every one his ways,
And shall not break their ranks,” etc.
It is remarkable that Volney, who had no intention of illustrating the truth of Scripture, has given a description of locusts, as if he meant to confirm the truth of what is here said. “Syria,” says he, “as well as Egypt, Persia, and almost all the south of Asia, is subject to another calamity no less dreadful (than earthquakes); I mean those clouds of locusts so often mentioned by travelers. The quantity of these insects is incredible to all who have not themselves witnessed their astounding numbers; the whole earth is covered with them for the space of several leagues. The noise they make in browsing on the trees and herbage may be heard to a great distance, and resembles that of an army foraging in secret” (Travels in Egypt and Syria, vol. i. pp. 283, 284).