John Calvin Commentary Psalms 1:4

"The wicked are not so, But are like the chaff which the wind driveth away." — Psalms 1:4 (ASV)

The Psalmist might, appropriately, have compared the ungodly to a tree that quickly withers, as Jeremiah likens them to the heath which grows in the wilderness (Jeremiah 17:6). But not considering this figure sufficiently strong, he debases them by employing another, which represents them in a still more contemptible light. And the reason is that he does not focus on the prosperous condition of which they boast for a short time, but his mind is seriously pondering the destruction that awaits them and will eventually overtake them.

The meaning, therefore, is that although the ungodly now live prosperously, yet soon they will be like chaff. For when the Lord has brought them low, he will drive them here and there with the blast of his wrath. Moreover, 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 rises high and appears to great advantage, like a stately tree, we may rest assured that he will be just as chaff or refuse, whenever God chooses to cast him down from his high position with the breath of his mouth.