There is an intensification of contrast between the wicked and the righteous in the first 40 psalms that begins to thin out and give way as the book progresses to the last 50 psalms, which focus on praise. There is a movement in the book from conflict to blessing, from lament to praise. When you get to the last psalm in the book, Psalm 150, there is absolutely no mention of the wicked. They’re gone.
Living in a wicked world presents challenges for people attempting to walk the way of righteousness. We are constantly bombarded with competing images of the good life, and the wicked often appear to be flourishing. For this reason, God’s people must delight themselves in God’s Word, meditating on Scripture to the degree that our hearts are formed by the right images.
And this is exactly what the book of Psalms is for us. As the Five Books of Moses are the Torah for the mind, so the Five Books of Psalms are the Torah for the heart; God intends for this collection of psalms to form and shape our image of what it means to be blessed, our image of what it means to flourish as we meditate on these songs, as we muse on the music of God-inspired psalms.
This is the difference between a righteous person and a wicked person—what forms our image of blessedness.