I use this Psalm often as a source of strength and direction, and I want to make sure I understand it.
If you find in Psalm 37 “a source of strength and direction,” then you certainly do understand it. I won't print it here, because it's quite long, but it's a ringing assurance that, no matter how “the wicked” may seem to flourish, “they will soon fade like the grass, and wither like the green herb.” It was apparently a favorite psalm of Jesus, as well; note verse 11 – “the meek shall inherit the land” – and compare it to Matthew 5:5 – “Blessed are the meek, for they shall inherit the earth.”
Metaphysically, Psalm 37 powerfully affirms one of our most basic and important universal spiritual principles. Choices have consequences. And negative, fear-based choices have negative, fear-based consequences. Those consequences may seem delayed from our limited human perspective, but they will occur in divine time. We may not have the dubious pleasure of seeing those negative consequences, but we may be sure they will occur.
It may seem a little vengeful for the good to insist on negative consequences for the wicked. But that's not really the point. The point is, we must know and believe without hesitation or question that spiritual principles are absolute; otherwise we could easily allow ourselves to be talked into choosing what seems to be a quick pleasure in the hope or assumption that there won't be consequences. There will.
So it's really a call to know our truth, and to have faith in the absolute love that is God. “Depart from evil, and do good; so you shall abide forever. For the Lord loves justice; he will not forsake his faithful ones” (Psalm 37:27-28 NRSV).