In this post, we will look at thesis 5 and thesis 6 of the Heidelberg Disputation.
The works of men are thus not mortal sins (we speak of works which are apparently good), as though they were crimes.
For crimes are such acts which can also be condemned before men, such as adultery, theft, homicide, slander, etc. Mortal sins, on the other hand, are those which seem good yet are essentially fruits of a bad root and a bad tree. Augustine states this in the fourth book of Against Julian (Contra Julianum).
The works of man appear to be morally good and beneficial. This apparent goodness of our works seduces us into placing our trust in self rather than God.
The works of God (we speak of those which he does through man) are thus not merits, as though they were sinless.
In Eccles. 7[:20], we read, “Surely there is not a righteous man on earth who does good and never sins.” In this connection, however, some people say that the righteous man indeed sins, but not when he does good. They may be refuted in the following manner: “If that is what this verse wants to say, why waste so many words?” or does the Holy Spirit like to indulge in loquacious and foolish babble? For this meaning would then be adequately expressed by the following: “There is not a righteous man on earth who does not sin.” Why does he add “who does good,” as if another person were righteous who did evil? For no one except a righteous man does good. Where, however, he speaks of sins outside the realm of good works he speaks thus [Prov. 24:16], “The righteous man falls seven times a day.” Here he does not say, “A righteous man falls seven times a day when he does good.” This is a comparison. If someone cuts with a rusty and rough hatchet, even though the worker is a good craftsman, the hatchet leaves bad, jagged, and ugly gashes. So it is when God works through us.
The good works of man are not criminal, but are nevertheless mortal sins because they are human works. Since we are fallen creatures, our works are not truly good. Even those works of God in us are not sinless. But the righteous are justified as both saint and sinner (simul iustus et peccator).