Hi, I've most recently spent almost 20 years as an RC. Now, I'm converting to Lutheranism. I've seen 1) Law/Gospel, and 2) Theology of the Cross/Theology of Glory, spoken of numerous times. What are they, please?
Both are supremely important, and also related to one another. Let's tackle Law and Gospel first, because it is perhaps the most important thing to try and understand here. And where I haven't been complete or clear enough, I'm sure others will fill in the gaps and offer more clarification.
The dichotomy of Law and Gospel is, essentially, the heart of Lutheran biblical exegesis and how we "do" theology.
The best summation of these comes from Thesis 26 of Luther's Heidelberg Disputation,
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The law says, 'do this', and it is never done. Grace says, 'believe in this', and everything is already done."
In other words the Law is what God commands. The Gospel, on the other hand, is what God promises.
So the commandments, such as "Do not murder", "Love the Lord your God", "Love your neighbor as yourself", etc are Law. This is what is commanded of us.
Also, from the Epitome of the Formula of Condord,
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1. We believe, teach, and confess that the distinction between the Law and the Gospel is to be maintained in the Church with great diligence as an especially brilliant light, by which, according to the admonition of St. Paul, the Word of God is rightly divided.
2. We believe, teach, and confess that the Law is properly a divine doctrine, which teaches what is right and pleasing to God, and reproves everything that is sin and contrary to God's will.
3. For this reason, then, everything that reproves sin is, and belongs to, the preaching of the Law."
The chief purpose or use of the Law is to curb and restrain evil, i.e. what is right against what is wrong (still quoting from the Epitome of the Formula of Concord),
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Since the Law was given to men for three reasons: first, that thereby outward discipline might be maintained against wild, disobedient men [and that wild and intractable men might be restrained, as though by certain bars];"
And also to serve as a mirror to show men their own trespasses and sins, as a man looking into a mirror,
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secondly, that men thereby may be led to the knowledge of their sins;"
And also, to provide proper instruction for how the godly ought to conduct themselves,
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thirdly, that after they are regenerate and [much of] the flesh notwithstanding cleaves to them, they might on this account have a fixed rule according to which they are to regulate and direct their whole life,"
So the Law asserts what is righteous against unrighteousness, reveals our own unrighteousness and the shame of our sin which is why we all stand equally condemned under the Law, and also that we might have that rule by which to direct our lives as God's people.
The Law does not save, cannot save, and will never save anyone. Therefore even though the Law tells us how we ought to live, and we must do it, we always have to go back and look at the first two uses, especially the second use: The Law reveals our sin. So even though we are born again, having been made alive in Christ, nevertheless we remain sinners while alive in this body, and so even as we seek to live lives of good works as God commands we fail, we sin, and we falter. So that no one can ever claim for himself that he is righteous by his own efforts. For as soon as a man thinks himself righteous by his own efforts the Law falls down upon him as an unbearable weight, crushing him, showing forth the depths of unrighteousness.
The irony is that the more we try to be righteous, the more unrighteous we show ourselves to be. The harder we try to be good, the more depraved we find ourselves to be. For all have fallen short, and the wages of our sin is death.
Therefore the Law is powerless to justify us, to render us righteous before God. All stand condemned under the Law.
The Gospel, however, is not like the Law, because where the Law says "do this" the Gospel says "trust this" because what is promised is already done.
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4. But the Gospel is properly such a doctrine as teaches what man who has not observed the Law, and therefore is condemned by it, is to believe, namely, that Christ has expiated and made satisfaction for all sins, and has obtained and acquired for him, without any merit of his [no merit of the sinner intervening], forgiveness of sins, righteousness that avails before God, and eternal life."
The condemned sinner is made alive by the Gospel, for here the sinner receives, as pure grace without any merit, the work and righteousness of Jesus Christ and the full pardon and forgiveness of sins. So that in Christ we are, indeed, "the very righteousness of God" (2 Corinthians 5:21). This is that righteousness which is apart from the Law, that is, apart from all our efforts and works to try and obey the Law (which we cannot do on account of our sin), the righteousness which is Christ's alone who alone is "Just and Justifier" of the unjust (Romans 3:26) through faith. Not a faith which is of ourselves, but that faith which is of God's grace, as pure gift, not of ourselves (Ephesians 2:8) so that no one may boast in his works (Ephesians 2:9).
So that the Gospel is, indeed, "the power of God to save all who believe" (Romans 1:16) because "by it the justice of God is revealed, the justice which is through faith" (Romans 1:17). For here "God demonstrates His love for us in that while we were yet still sinners, Christ died for us." (Romans 5:8)
So here we see that the Law is God's commandment for righteousness which we, on account of sin, fail to do, and on this account stand hopelessly condemned under the Law.
And we see here that the Gospel is God's good, loving, compassionate, kind, and gracious word and promise to us that we sinners are received as children and heirs through Christ who accomplished all things for us, by His work and righteousness alone. So that all who belong to Christ are indeed saved, justified, and belong to God forever. Christ alone has accomplished this, and God in His mercy gives us all these good things through Christ by the power of the Holy Spirit. So that we can indeed give thanks to God for what He has done, knowing that we have God as our Father who loves us, keeps us, and saves us both now and on the Last Day.
-CryptoLutheran