Since we have been justified by faith, we have peace with God. Paul states a fact here, not a wish. Peace with God is not a hope but a reality since the cross.
Accusation tries to disturb this peace. It says: you are not good enough for peace with God. But Paul says: peace stands because righteousness stands. And righteousness stands through faith, not through works.
When inner voices say today: you have not earned peace, answer: Peace stands. Not because I am perfect but because Christ fulfilled everything.