THE GUARANTEE OF PEACE.
It is obvious from this that the apostle is inviting everyone who has understood that he is justified by faith and not by works to that peace which passes all understanding,[1] in which the height of perfection consists. But let us investigate further in order to see what the apostle means when he talks about peace, and especially about that peace which is through our Lord Jesus Christ. Peace reigns when nobody complains, nobody disagrees, nobody is hostile and nobody misbehaves. Therefore, we who once were enemies of God, following the devil, that great enemy and tyrant, now, if we have thrown down his weapons and in their place taken up the sign of Christ and the standard of his cross, have peace with God. But this is through our Lord Jesus Christ, who has reconciled us to God through the offering of his blood.
Let us therefore have peace, so that the flesh will no longer war with the spirit, nor will the law of God be opposed by the law of our members. Let there not be in us yes and no, but let us all agree, let us all think alike, let there be no dissension either among ourselves or between us and others outside our ranks, and then we shall have peace with God through our Lord Jesus Christ. But let it most definitely be known that anyone in whom the vice of wickedness is found can never have peace. For as long as he is thinking how he can hurt his neighbor, as long as he seeks after ways of causing harm, his mind will never be at peace.
But if you ask me how a righteous man can have peace when he is attacked by the devil, who maintains his wars of temptation, I would say that such a man has greater peace than anyone else. . . . For the apostle says that we have peace with God knowing full well that war against the devil is a guarantee of peace with God. We shall have even greater peace with God if we continue our active hostility toward the devil and fight against the vices of the flesh. For the apostle James says: Resist the devil and he will flee from you; draw near to God and he will draw near to you.[2] You see that James too felt that he was getting closer to God by resisting the devil.
Commentary on the Epistle to the Romans