“Therefore, having been justified by faith we have peace with God through our Lord Jesus Christ” (Rom. 5:1)
The “therefore” refers [in Romans 4] to Abraham’s faith in the promise that he should have a son- a child of faith. But the same faith that resulted in the birth of Isaac, also brought righteousness to Abraham. Therefore, the righteousness of faith is as real as was the son that was born to him through faith.
What is peace? Most people have the idea that it is a sort of ecstatic feeling. They think that peace with God means and indescribable heavenly feeling. They always look for that imaginary feeling as evidence that they are accepted with God. But peace with God means the same thing that it means with people: it means simply the absence of war. As sinners we are enemies of God.
He is not our enemy, but we are His enemies. He is not fighting against us, but we are fighting against Him. How then may we have peace with Him? Simply by ceasing to fight, and laying down our arms. We may have peace whenever we are ready to stop fighting.
Note that when we have peace with God we are not simply at peace with Him, but we have His peace. This peace has been left on earth for us; for the Lord has said, “Peace I leave with you, My peace I give to you” (Jn. 14:27). He has given it to us. It is ours, therefore, already. It has always been ours. The only trouble has been that we have not believed it.
As soon as we believe the words of Christ, then we have in very deed the peace which He has given. And it is peace with God, because we find the peace in Christ, and Christ dwells in the bosom of the Father (Jn. 1:18).
Waggoner, Waggoner on Romans, pp. 92,93