Further, the preacher is not simply to convey information; still less is he there to entertain. His task is far too serious for either of these: he is exposing a current reality (the human tendency to seek to be right with God through self-righteousness) and creating a new reality (where we are clothed with the crucified Christ’s righteousness). Thus, he is to show people that all their righteousness is as filthy rags and as reliable a leaning post as a spider’s web; and that, counterintuitive and countercultural as it may be, true righteousness, mercy, and grace are to be found in the filthy and broken corpse of a man condemned as a criminal to hang on a cross. This is the preaching of law and gospel, and it carries with it transformative power.
Because God’s Word addresses human beings in this way, it can never be a morally indifferent force. It challenges us at the most basic level of our being, in terms of our very identity.
Carl Trueman, Luther on the Christian Life