“Many are persuaded that Paul deals in the above text [II Cor. 3:10] with the ceremonial righteousness which is now repealed; yet he is speaking of the whole law, and comparing law with grace, not law with law. … In brief then, let us point out that there are two ministries of preaching; one of the letter, the other of the spirit. The letter is the law, the spirit is grace. The first belongs to the Old Covenant, the second to the New. The glory of the law is the knowledge of sin; the glory of the Spirit is that revelation, or knowledge, of grace which is faith. Therefore the law did not justify: indeed, since human frailty found it unbearable, grace is veiled by it on Mount Tabor even to the present time.
“… I say, therefore, that just as the law of the Decalogue is good if it is observed-that is, if you have faith, which is the fulness of the law and of righteousness-so also it is death, and wrath, and no good to you if you do not observe it-that is, if you do not have faith. This is so, no matter how many good works you do-for the righteousness of the law, that is, of the Ten Commandments, is unclean and abolished by Christ even more than is [the righteousness] of ceremonies. It is precisely the righteousness of the law which is the veil over the face of Moses, and which the glory of faith removes” (“Against Latomus,” LW 32, 177, 178).