Let the wicked prosper but instead of getting frustrated at their prosperity let us leave it to God to deal with them. Let the righteous conserve their energies to do what is right and not expend it on dealing with the wickedness of the wicked!
The presence of wicked people in society is destructive. The psalmist in Psalm 37 knows well that these are people who borrow but never pay back (Verse 21). The wicked are those who oppress the weak and the innocent (Verse 14). For reasons that we may never know it is true that the wicked have outnumbered the righteous in every generation. To expect to create a world where there is no wickedness would be a mere utopia. The wickedness is there to stay. One wicked man goes, but two will come in his place, and the wickedness will always continue.
By nature, the righteous person cannot tolerate wrong. They burn with righteous anger. Especially when we see the wicked persons succeed in their wicked ways, we become frustrated and sometimes may question the justice of God (See verse 7). The psalmist has some advice for those who, in their relationship with God and in their involvement in the society are righteous. His advice is for those who would like to see righteousness established and prevail.
"Do not fret" is the advice. Put it another way: let the wicked not make you angry by their wickedness. The foremost reason is that there is no need to fret. The wicked are not here for ever (Verses 1-2). They do exist but only for a short while. They are the most transient of all: like grass that withers. Why should we waste our energy being angry while they are already under God's wrath and will be consumed in at the proper time affirms the thought of verse 2 that the wicked will not last forever. Thus, our fretting is unnecessary.
Secondly, fretting could lead to sin; meaning it could turn a righteous to wicked. In other words, it is counterproductive. This is what we find in verse 8. By being angry at the wicked, and in their zeal to deal with wickedness, the righteous may be tempted to do things are not pleasing to God.
Thirdly, it is better to be content with what one has than being unhappy with what the wicked has gathered with his wickedness. This will take away any reason to be unhappy with the prosperity of the wicked people. At the same time, the righteous is cared for by the Lord. This thought is scattered throughout the psalm in verses 16, 18, 19 etc.
Let the wicked prosper but instead of getting frustrated at their prosperity let us leave it to God to deal with them. Let the righteous conserve their energies to do what is right and not expend it on dealing with the wickedness of the wicked!