14 But when I saw that their conduct was not in step with the truth of the gospel, I said to Cephas before them all, “If you, though a Jew, live like a Gentile and not like a Jew, how can you force the Gentiles to live like Jews?”
15 We ourselves are Jews by birth and not Gentile sinners; 16 yet we know that a person is not justified by works of the law but through faith in Jesus Christ, so we also have believed in Christ Jesus, in order to be justified by faith in Christ and not by works of the law, because by works of the law no one will be justified.
17 But if, in our endeavour to be justified in Christ, we too were found to be sinners, is Christ then a servant of sin? Certainly not! 18 For if I rebuild what I tore down, I prove myself to be a transgressor. 19 For through the law I died to the law, so that I might live to God. 20 I have been crucified with Christ. It is no longer I who live, but Christ who lives in me. And the life I now live in the flesh I live by faith in the Son of God, who loved me and gave himself for me. 21 I do not nullify the grace of God, for if righteousness were through the law, then Christ died for no purpose.
Paul's doctrine of grace, however, raised problems for the Jewish mind. The Apostle's immediate concern here is with the law, and the believer's relationship to it. To him living under the law and living unto God are mutually exclusive. He dies to the law, as to everything else in the old life, in the death of Christ, and lives unto God, in the Spirit. But the Jews felt that dismissing the law from salvation was deadly dangerous and that it led to antinomianism - sinning that grace may abound (cf Romans 6:1). Their argument in 17ff is as follows (following J.R.W. Stott): 'Your doctrine of justification through faith in Christ only, apart from the works of the law, is a highly dangerous doctrine. It fatally weakens a man's sense of moral responsibility. If he can be accepted through trusting in Christ, without any necessity to do good works, you are actually encouraging him to break the law, which is the vile heresy of antinomianism'. But this, Paul maintains, is entirely to misunderstand the doctrine of free grace and of justification. Justification is not a legal fiction, in which a man's status in God's sight is changed without any corresponding change in his character. Indeed, as 17 makes clear, we are justified in Christ (not 'by Christ' as in AV), and 'in Christ' we are new creatures (2 Corinthians 5:17). We could put it this way: the picture Paul has of the gospel is like a parabola - the downward movement of Christ to the Cross, then the upward movement to the Father's right hand (cf Philippians 2:5ff). When this 'movement' touches a man's life and takes it up into itself, the miracle of grace takes place. He is incorporated into Christ - and into His finished work, in the sense that he partakes of its power and virtue. When we look at conversion in this way, we see that it involves not only justification, but also a being brought down into the death of Christ, and up into newness of life in Him. Thus, to have faith means not only to be justified, but also to be crucified - hence the tremendous assertion in 20. To repent, to turn one's back on the old life, is to die - and yet, it is not to die, but to live. We live, yet it is the life of Another within us - Christ's life, by the Spirit. This, we must surely see, is rebirth by the Spirit, the reception of the Spirit by which we become new creatures, who will not continue in sin.