A killer, seasonally appropriate quote from Werner Elert’s classic pamphlet “Law and Gospel”:

“Obviously the words of Christ [from the Sermon on the Mount] cannot be twisted in order to say that by heightening the demands of the law he sought only to demonstrate the impossibility of fulfilling it, and thus from the very outset to induce his hearers to capitulate. The law is and remains a demand. It is inviolably valid. Not an iota will pass from it. It ought to be and must be fulfilled (Matt. 5:18).

“It is another question, however, whether with this heightened interpretation Christ intended to say that his hearers actually had fulfilled the law. If he really did intend to say that, then there would be a contradiction between him and Paul. But that would be an even worse twisting of his words than the previous one. Exactly the opposite is correct. The proof is found precisely in his treatment of the decalogue commandments. For when he transposes the criteria for fulfillment from the external to the internal, he presupposes his hearers know what feelings of hatred and evil lusts are. Here we already have the lex semper accusat. What murder and adultery are, in the sense of acts that transgress the commandments, one can also learn merely by being told. However, what hatred and evil lusts are we could not even imagine if we had not experienced them ourselves. Accordingly, for the man who receives the heightened interpretation of the decalogue as validly directed toward himself, it exposes his own inner nature, and demonstrates to him that his opposition to God’s law is not only possible, but actual. At that point no further self-examination is necessary. The man who understands what Christ means by hatred and impure desires testifies by the mere fact of this understanding that he is already guilty of this transgression.

“The law always accuses. Christ exempted no one from this verdict. Proof of this can be seen in his call, directed to everyone, for repentance from the heart (Makr 1:15 in conjunction with Luke 13:3-5). The “Our Father”, designed for all to pray, presupposes also that all are guilty (Matt. 6:12). Therefore also in the interpretation which the law receives from Christ it always exposes man’s sin. There is no situation imaginable, so long as the law reigns over us, where it would not exercise this accusatory function.”