We must take our definition from the etymology of the word. When men grasp the conception of things with the mind and the understanding they are said “to know,†from which the word “knowledge†is derived. In like manner, when men have an awareness of divine judgment adjoined to them as a witness which does not let them hide their sins but arraigns them as guilty before the judgment seat – this awareness is called “conscience.†It is a certain mean between God and man, for it does not allow man to suppress within himself what he knows, but pursues him to the point of making him acknowledge his guilt. This is what Paul means when he teaches that conscience testifies to men, while their thoughts accuse or excuse them in God’s judgment (Rom. 2:15-16). A simple awareness could repose in man, bottled up, as it were. Therefore, this feeling, which draws men to God’s judgment, is like a keeper assigned to man, that watches and observes all his secrets so that nothing may remain buried in darkness. Hence that ancient proverb: conscience is a thousand witnesses. By like reasoning, Peter also put “the response of a good conscience to God†(1 Peter 3:21) as equivalent to peace of mind, when, convinced of Christ’s grace, we fearlessly present ourselves before God. And when the author of of The Letter to the Hebrews states that we “no longer have any consciousness of sin†(Heb. 10:2), he means that we are freed or absolved so that sin can no longer accuse us.
Therefore, just as works concern men, so the conscience relates to God in such a way that a good conscience is nothing but an inward uprightness of heart. In this sense, Paul writes that “the fulfillment of the law is love, out of a pure . . . conscience and faith unfeigned†(1 Tim. 1:5 p.). Afterward, in the same chapter, he shows how much it differs from understanding, saying that certain ones “made shipwreck of faith†because they had “forsaken a good conscience (1 Tim. 1:19). For by these words he indicates that is a lively longing to worship God and a sincere intent to live a godly and holy life. (Institutes, IV. x. 3-4.)
A couple of points are worth noting. One is the importance (there goes that squishy word) of justification to a clean conscience. Since justification is precisely a verdict of not guilty, that benefit alone can give the wounded and grieved conscience what it so desperately needs. I am not saying the doctrine does this logocentrically – as if propositions have consequences – or that this happens apart from the work of the Spirit. I am saying that a guilty conscience is important for all people because of the reality and pressing demands of the law. To have that burden lifted because of the perfect righteousness of Christ imputed to us by faith alone is an amazingly liberating moment and life.
The second point is how much Calvin sees love and holy living springing from this forensic reality of a clear conscience. Conscience goes far down in all of us thanks to being created in the image of God. So to change that legal torments that goes to the core of our being as sinners may also involve something truly renovative. At least, it is responsible to say that the significance of conscience in the life of every person means that justification can in no way be merely a book keeping matter, as if our account is credited with Christ’s righteousness way over there but then we need to have a moral transformation way deep down over here inside us for salvation to play out. Justification solves the guilty conscience problem. It’s a remedy for what is basic and deep down in each human being.



