Second, Paul summarizes the central point of disagreement in the dispute between himself and those who forced the Jewish Christians to separate from Gentile Christians. His summary of his opponents' accusations against him consists of two premises and a conclusion: first premise—if, while we seek to be justified in Christ; second premise—it becomes evident that we ourselves are sinners; conclusion—does that mean that Christ promotes sin? (v. 17). From the perspective of the opponents, while Paul was seeking justification in Christ, he was at the same time living like a sinner; therefore Christ promoted sin. In other words, if his identification with Christ led him into sin, then Christ was the cause of his sin.

Certainly Paul would accept the first premise. As he clearly states in verse 16, all Jewish Christians knew that they were justified not by observing the law but by faith in Christ. But would Paul have accepted the second premise of this accusation? That depends on how we interpret the second premise. The key to the interpretation of this premise is the meaning of the word sinners. Does this term refer to the preconversion status or the postconversion status of Jewish Christians? It might appear from the logic of verses 15-16 that sinners referred to the recognition of Jewish Christians before their conversion that they too, like Gentiles, were sinners and hence could attain justification only through faith in Christ. But this line of interpretation fails to provide a reason for the accusation that Christ promotes sin. After all, the recognition of one's sinful position and total dependence on God's grace was a basic tenet in Jewish faith. Within Judaism, the acknowledgment of sin and the forgiveness of sin through the sacrificial system did not imply that the sacrificial system promoted sin.

The interpretation of sinners as a reference to a preconversion recognition of sin also fails to fit the context of this passage. Paul is writing these words in response to the conflict in Antioch. The criticism of Paul, Peter and the other Jewish Christians in that conflict was not because of their admission of sin before or in their conversion experience, but because of their practice of breaking Jewish purity laws by eating with Gentiles. When we keep this context in focus, it becomes clear that the term sinners refers to postconversion activity. The Jewish Christians in Antioch were accused of sinning after their commitment to Christ. They were not accused of all kinds of immoral behavior: sexual immorality, deceitfulness, stealing and so forth. They were accused of a specific sin: breaking the law by eating with Gentiles. Such behavior put them on the same level as Gentiles; they were sinners outside the covenant people of God.

This interpretation makes sense of the accusation that Christ promotes sin. The accusers understood correctly that the Jewish Christians were eating with Gentile Christians because of their common faith in Christ. Therefore their faith in Christ led them into the sin of breaking Jewish purity laws. If identification with Christ promoted unlawful identification with Gentiles, then, it was argued, Christ promotes sin.

Paul frames this argument of the opponents in the form of a question and counters it with an indignant Absolutely not! (v. 17). Paul refuses to accept the conclusion that Christ promotes sin because he refuses to accept the second premise. From the perspective of his accusers, eating with Gentiles is sinful, because the law forbids it. But from Paul's perspective, eating with Gentile Christians is not sinful, because the gospel demands it. Withdrawal from table fellowship with Gentile Christians was hypocrisy; it was a violation of the truth of the gospel. The conclusion that Christ promotes sin is wrong, because what was judged to be sinful (eating with Gentiles) according to the law is not really sinful according to the gospel.

Paul's statement of the accusation leveled against his position in Antioch also reflects the argument of his opponents in the Galatian crisis. Just as the failure of Jewish Christians at Antioch to observe Jewish food regulations caused them to be demoted to the category of "Gentile sinners," so the failure of Gentile Christians at Galatia to observe circumcision kept them, it was argued, from being promoted to the category of the children of Abraham. The point of attack was the common failure of Jewish Christians at Antioch and Gentile Christians at Galatia to keep the law.

Paul's countercharge to the accusations leveled against him is stated in verse 18: if I rebuild what I destroyed, I prove that I am a lawbreaker. The object of the verbs rebuild and destroy must be understood from the context. In verse 16 Paul affirms that observing the law is not the basis of justification. In verse 17 he denies that the law can be used as a valid basis for criticizing his practice of eating with Gentile Christians. And in verse 19 he affirms that through the law he died to the law. So it is his past relationship to the law that has been destroyed and must not be rebuilt.

The law can no longer be used as the basis for judging the practice of Christians (v. 17). To rebuild the law means to reinstate the law for the supervision of the Christian life. If the law is reinstated, then the Christian is proved to be a lawbreaker. Some have interpreted Paul's argument to be against rebuilding the law on the grounds that rebuilding the law will prove him to be a lawbreaker. In other words, the transgression of breaking the law is admitted only if the law is reestablished. If the law is established for supervision of the Christian life, then eating with Gentiles is sin, since it is forbidden by the law.

If we keep the context in mind, however, we will see that the transgression referred to by Paul in verse 18 is actually the rebuilding of the law rather than the breaking of it. According to verse 14, Peter's real transgression was that he did not live consistently according to the truth of the gospel. The gospel had destroyed all essential distinctions between Jews and Gentiles and rendered inoperative all laws that upheld those distinctions. Whoever observed all the Jewish law—and so maintained such Jew-Gentile distinctions—violated the truth of the gospel. Duncan makes this point:

If it is regarded as "sin" for a Jewish-Christian to eat with a Gentile, it is sin only in the sense of a technical breach of a regulation; but if a Christian allows such a regulation to stand between him and eating with a brother-in-Christ, then he is breaking God's law in a much more heinous sense, for he is doing violence to the will of God as clearly revealed in Christ. (Duncan 1934:69)

In chapter 3 Paul develops the theological basis for his assertions here regarding the role of the law in the Christian life. Our study of that chapter will lead us to consider in more depth what Paul means when he asserts that "we are no longer under the supervision of the law" (3:25). We must note here, however, that the whole discussion of law and gospel is the result of a division between the Jewish and Gentile believers in the church. That racial division threatened the effectiveness of Paul's mission to the Gentiles. It is in defense of his God-given mission that Paul spells out the relationship between law and gospel. His goal is to prove that in Christ Jesus there is neither Jew nor Greek (3:28). The unity and equality of all believers in Christ is the foundational principle and overarching aim of Paul's entire argument.

Although it may be difficult to follow each step of his argument, we can at least appreciate the lengths to which he goes to defend the unity and equality of all believers in Christ. And the more we grow in our understanding of the steps in his argument, the more we too will be able to protect the equality and unity of all believers in Christ.