“The wicked are not so, but are like chaff that the wind drives away.” –Psalm 1:4
Verse four is what is sometimes called “the turn” in poetry. The Psalmist creates an image that contrasts the blessedness we’ve been observing in order to drive home the point and demonstrate the quality and fate of the damned.
It is an agricultural image of threshing and winnowing the wheat. In this process, the stalks of wheat are threshed and then thrown into the air where the chaff—the weightless and worthless fragments—is carried away by the wind, while the weighty and valuable corn falls into piles to be harvested.
The emphasis of this verse is ontological, however.
In other words, it is about what a man is rather than about what he experiences. It is true the life of the wicked is often characterized by uncertainty, one that is driven by the winds of the world.
But that is only because of what he is, chaff. The wicked are rootless, unlike the rooted tree; the wicked are fruitless, unlike the fruitful tree; the wicked are worthless, unlike the prosperous tree.