Saturdays with Calvin #62

Paul uniformly declares that the conscience can have no peace or quiet joy until it is held for certain that we are justified by faith. And he at the same time declares whence this certainty is derived—viz. when “the love of God is shed abroad in our hearts by the Holy Ghost,” (Rom. 5:5); as if he had said that our souls cannot have peace until we are fully assured that we are pleasing to God. Hence he elsewhere exclaims in the person of believers in general, “Who shall separate us from the love of Christ?” (Rom. 8:35). Until we have reached that haven, the slightest breeze will make us tremble, but so long as the Lord is our Shepherd, we shall walk without fear in the valley of the shadow of death (Ps. 23). Thus those who pretend that justification by faith consists in being regenerated and made just, by living spiritually, have never tasted the sweetness of grace in trusting that God will be propitious. 

Institutes of the Christian Religion 3.13.5 John Calvin, translated by Henry Beveridge, Hendrickson, pg. 501.