The Law of God & the Believer [A Reformed Perspective]
Pastor Jay post:
Typically Reformed Christians have always believed in the third use of the law. The third use of the law is that the moral laws of God or the Ten Commandments are morally binding on the Christian and a normative pattern for the Christian life.
The third use of the law teaches that the moral law becomes a rule of life for the believer. In the Geneva Catechism Calvin asks, “What is the rule of life which God has given us?” The answer, “His law.” Calvin says, “The law shows the mark at which we ought to aim, the goal to which we ought to press, that each of us, according to the measure of grace bestowed upon him, may endeavor to frame his life according to the highest rectitude, and by constant study, continually advance more and more.” 
One must guard the fact that this does not mean that one must keep the moral law of God in order to be justified as this would be salvation by works of the law, the very thing that Paul denounces so often in his writings (cf. Gal 2:16 | Rom 3:20-21). But although no one can be justified by keeping the moral law of God, this is not to say that the standard of the law has been abolished. The Christian ought to continue to aim at the moral law of God as his standard for sanctification (cf. Rom 3:31 | Rom 8:1-4). Consider what Thomas Schreiner in his commentary concerning Romans 3:31,which says, “Therefore do we abolish the law by faith God forbid we establish the law.” Schreiner says,
“The moral norms of the law still function as the authoritative will of God for the believers (Murray). The idea is not precisely that the law is fulfilled by faith in Christ (contra moo) but rather that those who have faith in Christ will keep the law. Paul does not expand on this point here, but as in 3:8 he touches upon a point that will receive more extended discussion later. He wants to guard against a common misunderstanding here: some have objected that if righteousness is not through the law then the law is abolished… Righteousness apart from the law’s commands does not mean that believers can dispense with the moral norms of the law.” 
Schreiner brings up a very important point. Just because we are not justified by the works of the law but we are justified by faith then we do not dispense with the moral law of God. But many in evangelicalism think exactly this. They reason that since one is not justified by works of the law but only through faith then the New Testament Christian does not have anything to do now with the moral law of God. This is an error in understanding not only what the Bible teaches as a whole but also an error in the proper understanding of the nature of saving faith and of the effects of regeneration.
Jeremiah 31:31-34 shows that when we are regenerated then God writes his laws upon our hearts and puts them in our minds. But what law is he speaking of here in Jeremiah? The law that he is speaking of is the moral law of God or what is known as the Decalogue (the Ten Commandments). These are the moral laws of God that show us what God requires of his creatures in every age. The difference of the Old Covenant from the New Covenant is that God takes those commands that were written by the finger of God on tablets of stone and now writes them on the fleshly tablets of our heart (2 cor 3:3). The Christian now has an internal work of God in his soul and he intuitively knows what pleases and displeases God. He delights in the holiness of God as it is manifested in his law. The Law flows from the nature of God through the finger of God and becomes engraved on stones (Exod 31:18) but in the New Covenant God’s moral precepts are placed in human hearts via regeneration of the Spirit. What an awesome idea that the moral law of God which flows from God’s very nature revealed to us through tablets of stone written by the finger of God (Exod 31:18), and now these same moral precepts flow directly into the human hearts engraved on the fleshly tablets of our hearts by the Spirit of God (Jer. 31:31-34). God wrote his moral law on tablets of hard stone by his finger in the Old Covenant but in the New Covenant he writes his laws on fleshly soft hearts with the Holy Spirit.
Therefore true salvation is anything but anti-nomian. Those who are truly saved will do as Paul did and delight in the law of God in his inner man (Rom 7:22). They will have been transformed from law haters (Romans 8:7-8) into law lovers ( Psalm 119:113). They will go on to do good works that are in keeping in conformity to the moral law of God (James 2:14-21), and will be guided by the Holy Spirit to do the things which please him (Ezek 36:26-28).
Therefore we do not want to give up this doctrine of the third use of the law. It is vital for protection against anti- nomianism which is a problem in every age. If we give up this doctrine we will bring carnality into the church, give false assurance of salvation to carnal professing believers and weaken the power of the gospel. Some may falsely suppose that they are protecting the gospel by denouncing this doctrine of the third use of the law but they are in essence compromising the gospel by cheating it of its power. The gospel has the power to save and to transform from within. God’s people will progress in holiness until they are called home to their Lord. We must be confident in God’s ability to do these things and learn to wait upon him and his grace (Phil 1:3-4).
 Article by Joel Beeke found on the website www..monergism.com.
 Thomas R. Schreiner, Romans, in Baker Exegetical Commentary on the New Testament, (Grand Rapids: Baker Academic, 1998), 208.