4. The ungodly are not so; but are like the chaff which the wind driveth away.

The Psalmist might, with propriety, have compared the ungodly to a tree that speedily withers, as Jeremiah likens them to the heath which grows in the wilderness, (Jeremiah 17:6) But not reckoning this figure sufficiently strong, he debases them by employing another, which represents them in a light still more contemptible: and the reason is, that he does not keep his eye on the prosperous condition of which they boast for a short time, but his mind is seriously pondering on the destruction which awaits them, and will at length overtake them. The meaning, therefore, is, although the ungodly now live prosperously, yet by and by they shall be like chaff; for when the Lord has brought them low, he shall drive them hither and thither with the blast of his wrath. Besides, by this form of speech, the Holy Spirit teaches us to contemplate with the eye of faith, what might otherwise seem incredible; for although the ungodly man rise high, and appear to great advantage, like a stately tree, we may rest assured that he will be even as chaff or refuse, whenever God chooses to cast him down from his high estate, with the breath of his mouth.