These verses follow a long section on justification by faith. Paul concludes chapter 4 with the fact that Christ's resurrection was God's evidence that Christ's work was accepted and thus ensures our justification.
The word "therefore" at the beginning of chapter 5 shows that the immediate benefit of justification is that we have peace with God. This is justification by faith's practical influence on the lives of those justified. Paul says in Romans 8:6-7:
For to be carnally minded is death, but to be spiritually minded is life and peace. Because the carnal mind is enmity against God; for it is not subject to the law of God, nor indeed can be.
This plainly states that the sinner is the enemy of God, and the state of a sinner's mind is far from peace. It is at war, and his sinning proves the warfare, the rebellion in his mind. He is often agitated, alarmed, and trembling and feels alienated from God. God is not in all his thoughts (Psalm 10:4, KJV). Isaiah 57:20-21 explains:
But the wicked are like the troubled sea, when it cannot rest, whose waters cast up mire and dirt. "There is no peace," says my God, "for the wicked."
The sinner trembles when he thinks of God's law. He fears His judgments and is alarmed when he considers hell. But as God moves a person toward conversion, He reveals His willingness to be reconciled through His Son's sacrifice. Through faith and repentance, the obstacles arising from God's justice and law disappear, and He is willing to pardon and be at peace. When the sinner embraces it, this process produces peace of mind, a peace the world cannot give or take away because the world is powerless over sin. This peace is a work, a product, of the Spirit of God by which the sinner has been called and led to this point.
John W. Ritenbaugh
The Fruit of the Spirit: Peace