Fret not yourself because of evildoers;
be not envious of wrongdoers!
For they will soon fade like the grass
and wither like the green herb.
Contrasting righteousness with wickedness gives us warning and encouragement. Observing the end of wicked living has power to call us to God. It does not matter how long or how happy the lives of the wicked seem to be. The truth is that they will give account of themselves before a holy God, and in the end their lives will be as fading and as short as a field of grass that flourishes for a short summer but then browns and is cut down. All throughout this thirty-seventh psalm, king David contrasts the rewards of trusting God in righteousness with the bleak judgment outcomes that come to those who live for wickedness.
The psalm begins with two negative commands... not a popular way to preach today. There is power in these warnings however that we should understand. We should not worry about the apparent success of evil doers. That seeming happiness is short-lived. We should not envy the lives of those who do wrong. Their glib attempts at happiness will wither over time. God will punish the evil and reward the good. And those who disobey Him will fade away and wither like dying plants.
Sin leads to death. So evil will make only decay. It is the reason that entropy, sickness, and death are part of life on planet earth. And nobody escapes this reality.
But there is a better experience. The hope of God's reward for trusting Him is the only way out of the declining future that is life. We must believe God, reject evil, choose good, and find life. God has promised we can dwell safely (Psalm 37:3), have the desires of our heart by delighting in Him (Psalm 37:4), know His justice (Psalm 37:6), inherit what evil doers forfeit (Psalm 37:8), find peace (Psalm 37:11), know abundance in lean times (Psalm 37:19), and find joy in giving back to others with the blessings that we gain from God (Psalm 37:21). I will take abundant hope over a withering loss every day! And I'll do it by heeding negative examples for the better.