Mark the blameless man, and observe the upright; for the future of that man is peace.
Throughout the 37th Psalm, David contrasts those who do evil with those who do good. The evildoers may seem to prosper for a time, but ultimately they will receive the punishment they deserve if they don’t repent.
On the other hand, those who strive to live God’s way completely—blamelessly—will ultimately receive the blessings He promises.
Of course, all have sinned and no one is totally blameless. But through repentance and conversion, our past sins can be forgiven and we can start anew. We can commit ourselves to living the way Jesus Christ lived, according to God’s law—living the way that produces peace.