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. (Gal. 2.15-16)
In these verses we have the succinct statement of “Paul’s gospel,” that up to this point in the book he has only been referring to, but hasn’t enunciated. This is what he will be defending in the rest of the letter to the Galatians. The true gospel is justification through faith in Jesus Christ, not by works of the law. This is the only way to justification. There can never be justification by works. This justification is received by “believ(ing) in Christ Jesus.”
17 But if, in our endeavor 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. (Gal. 2.17-18)
When Paul speaks of being “found to be sinners” this refers to when others accuse Paul of being a “sinner” because he no longer follows the law and no longer seeks justification through it. It does not mean “found to be sinners” in the sense of not being truly justified by God or in the sense of not yet being perfected in holiness. When others make this accusation and say this about Paul, does that mean they are right, and that Christ is a “servant of sin” in that he allows Paul to live sinfully by not conforming to the law’s righteousness? The answer, Paul says, is “certainly not”.
The answer is “certainly not” because it is not sinful to reject conformity to the law as a means of attaining righteousness; exactly what Peter and the other Jews were unintentionally teaching by example in their hypocrisy.
“Rebuilding what I tore down” refers to seeking once again to be justified by the law rather than by faith in Christ. If Paul were to do this, the only result would be that he would be proven to be a transgressor, because the law can only condemn, it cannot save because Paul could never attain the righteousness that is by the law (see vs. 10-11)
When Peter and others were living hypocritically, they were doing this “rebuilding” of a law-based righteousness and Paul is criticizing them for it. Verse 21 sums up the issue at stake beautifully: “If righteousness were through the law, then Christ died for no purpose.”
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. (Gal 2.19-21)
Now Paul gives in contrast, the right approach to the law. Rather than using the law to seek to justify himself, he receives the condemnation of death that the law demands (“through the law…”). However, as v. 20 makes clear he receives this condemnation through his identification with Christ in his crucifixion.
The result of this is that he “dies to the law so that (he) might live to God.” Paul no longer lives, but Christ lives in him.
Then comes the key contrast that he had introduced in v. 16: between living by faith or by works of the law. Paul restates here that he lives “by faith in the Son of God who loved me and gave himself for me.” This is what many have been calling recently, a “gospel-centered life”. Perhaps we need to get beyond this buzzword and use the scriptural language of living by “faith in the Son of God.”
A “gospel-centered life”, or “living by faith in the Son of God” is trusting that Jesus’ death was my death and that my righteousness is not through a works-based righteousness, but rather through Christ.
This is what Paul implicitly says in v. 21 when he contrasts righteousness “through the law” with the purpose for which Christ died. He is implying that this purpose was to make us righteous.
The problem with the traditional holiness/second blessing understanding of Galatians 2.20 is that being “crucified with Christ” is not something that happens only in those certain believers who go through a crisis of surrender at some point after their conversion. This is true of every believer who is united with Christ by the Spirit. V. 20 is describing the indicative truth of what has happened to every true believer! So live by faith in the Son of God!