On Sin and Free Choice consists of three commonplaces. First, “On Original Sin” addresses the first sin of Adam and Eve (Genesis 3) and the terrible results of this primeval sin: the fact that all of Adam’s and Eve’s natural descendants lack original righteousness, are corrupted in their natures, and therefore stand guilty of God’s just judgment. The original sin is handed down from parents to children via the procreation. The healing from original sin, merited by Jesus Christ, begins to be applied in Holy Baptism.
Second, “On Actual Sins” deals with human statements, deeds, and desires that are against God’s moral law. Gerhard examines many categories of sins, and especially shows that even the wrongful desires within people are truly sins. The distinction between “mortal” and “venial” sin is shown to be biblical, but must be guarded from misunderstanding.
Third, “On Free Choice” speaks of how fallen human beings have some freedom of choice, but not the kind of freedom that could turn them towards God. The fallen human will freely chooses only things that are contrary to God, until the Holy Spirit converts a person to faith in Christ.