The law is used in two ways; first, for this worldly life, because God has ordained all temporal laws and statutes to prevent and hinder sin. But here some one may object: If the law hinder sin, then also it justifies. I answer: Oh! no, this does not follow; that I do not murder, commit adultery, steal, etc., is not because I love virtue and righteousness, but because I fear the hangman, who threatens me with the gallows, sword, etc. It is the hangman that hinders me from sinning, as chains, ropes, and strong bands hinder bears, lions, and other wild beasts from tearing and rending in pieces all that come in their way.
Hence we may understand, That the same can be no righteousness that is performed out of fear of the curse, but sin and unrighteousness; for the law binds mankind, who by nature are prone to wickedness, that they do not sin, as willingly they would.
Therefore this is the first point concerning the law, that it must be used to deter the ungodly from their wicked and mischievous intentions. For the devil, who is an abbot and prince of this world, allures people to work all manner of sin and wickedness; wherefore God has ordained magistrates, elders, schoolmasters, laws and statutes, to the end, if they can do no more, that at least they may bind the claws of the devil, and hinder him from raging and swelling so powerfully in those who are his, according to his will and pleasure.
Secondly, we use the law spiritually, as thus: To make transgressions seem greater, as St Paul says, or to reveal and discover to people their sins, blindness, and ungodly doings, wherein they were conceived and born; namely, that they are ignorant of God, and are his enemies, and therefore have justly deserved death, hell, God’s judgments, his everlasting wrath and indignation. But the hypocritical sophists in universities know nothing thereof, neither do those who are of opinion that they are justified by the law and their own works.
But to the end that God might put to silence, smother, suppress and beat down to the ground these mischievous and furious beats, he has appointed and ordained a particular Hercules with a club, powerfully to lay hold on such beasts, take them captive, strike them down, and so dispatch them out of the way; that is, he gave the law upon the hill of Sinai, with such fearful thundering and lightning, that all people thereat were amazed and affrighted.
It is exceeding necessary for us to know this use of the law. For he that is not an open and a public murderer, an adulterer, or a thief, holds himself to be an upright and godly man; as did the Pharisee, so blinded and possessed spiritually of the devil, that he could neither see nor feel his sins, nor his miserable case, but exalted himself touching his good works and deserts. Such hypocrites and haughty saints can God by no better means humble and soften, than by and through the law; for that is the right club or hammer, the thunderclap from heaven, the axe of God’s wrath, that strikes through, beats down, and batters such stock-blind, hardened hypocrites. For this cause, it is no small matter that we should rightly understand what the law is, whereto it serves, and what is its proper work and office. We do not reject the law and the works thereof, but on the contrary, confirm them, and teach that we ought to do good works, and that the law is very good and profitable, if we merely give it its right, and keep it to its own proper work and office.
The law opens not nor makes visible God’s grace and mercy, or the righteousness whereby we obtain everlasting life and salvation; but our sins, our weakness, death, God’s wrath and judgment.
The light of the gospel is a far different manner of light, enlightening affrighted, broken, sorrowful, and contrite hearts, and reviving, comforting, and refreshing them. For it declares that God is merciful to unworthy, condemned sinners, for the sake of Christ, and that a blessing thereby is presented unto them who believe; that is, grace, remission of sins, righteousness, and everlasting life.
When in this way we distinguish the law and the gospel, then we attribute and give to each its right work and office. Therefore, I pray and admonish all lovers of godliness and pure religion, especially those who in time are to be teachers of others, that with highest diligence they study this matter, which I much fear, after our time, will be darkened again, if not altogether extinguished. Martin Luther, Table Talk, Of The Law And The Gospel, CCXLLIV.