The Third Use of the Law is Not and Must Never Be Backdoor Legalism

The law of God has three uses:

The first use:  The curb given to man to inhibit sinful behavior and keep sin in check.

The second use:  The mirror which exposes our sin and drives us to repentance and faith in the gospel on account of the atonement of our sins by Christ on the cross.

The third use:  The guide which is for the Christian alone and instructs us on right living as we grow in holiness by faith.

The Christian, in his state of simul justus et peccator ("simultaneously justified and sinner"), always hears both the second and third use of the law when God's word is delivered to him... and both uses require the gospel. The second use works towards the gospel as it drives the sinner to repentance and faith in salvation on account of Christ where the third use works FROM the gospel where the Christian is freed from the threat of death by Christ's atonement and grows in love and holiness according to the Father's will by the power of the Holy Spirit.

In his sinful condition according to the flesh, all law slays man and convicts him because from the law comes the knowledge of sin (second use).

...but to stop there is to present an incomplete picture of sanctification that is not in accord with Scripture or Lutheran doctrine. From the gospel, the law is where the Holy Spirit works in the new creation by faith to create truly God-pleasing good works... the fruit of living faith (third use). These are the works that God created for his people to do by faith in the power of the Holy Spirit.

This is not a backdoor legalism but harmonizes the teachings of Romans and Galatians with that of James.

It is from the third use alone, that the new man can say what the Psalmist recorded by faith:

"Oh how I love your law! It is my meditation all the day. Your commandment makes me wiser than my enemies, for it is ever with me. I have more understanding than all my teachers, for your testimonies are my meditation. I understand more than the aged, for I keep your precepts."

...so the danger is not how the Holy Spirit chooses to use the law (second or third) in the heart of the Christian because both are necessary and good.  Both the mirror and the guide are God's righteous and gracious work in us. The danger is in man's application of the law for any reason that is delivered or received apart from the life-giving gospel.  That is not any proper application of the law, but a misapplication. That is what the error of legalism is... not the law's particular use per se, but any quest by man for righteousness apart from faith.

And so teaching the law for right living apart from the gospel and calling it "third use" is not correct.  The second use must drive us into the gospel and the third use must flow out of the gospel... every. single. time.  To ignore this is not any proper use of the law at all, but is a misuse of the law entirely.  Where the law is preached, taught, and received, the gospel must be always close at hand and the two must never be separated or confused.  The apostles did not separate or confuse them and neither should we.

The law that kills the old man according the flesh and the law that guides the new man according to the Spirit must be handled in the shadow of the cross with the work of the Spirit by faith in full and explicit view.  It is the greatest and most delicate task that any Christian will face and a skill that only the wisdom granted by the Holy Spirit can teach.  When this is not done, Christian consciences are seared and unrepentant sinners are confirmed in unrighteousness to their eternal peril.  This is not a fault or failure of God's law because the law in itself is a good and holy gift.  Instead the error is in our handling of God's gift to us... our sinful twisting and misuse of what God gives us for our own good that we pervert through carelessness or rebellion.

The solution is not to disregard the law entirely or ignore the biblical teachings regarding the law's role in our sanctification.  One does not take a gift of God and reject it simply because it is abused in the hands of sinful men and ignorant teachers.

The solution is to receive this good gift and meditate upon it daily as we handle God's word soberly and rightly so that Christ's disciples observe all that God has given to His church without confusion or error.