If our salvation is based on promise, not upon law, then what is the law for then? What is based on the law? What role does it have?
If salvation was based on promise, not on law, then what was the law for then (v. 19)? A reasonable question—the law was added for transgression until the promised seed should come. This law was mediated, but this means that “the Mosaic law” is not internal to the Trinity the same way the promise is (v. 20). Are the law and promise at odds then? Not at all—if law were trying to do what the promise did, it would have succeeded (v. 21). The law enrolled us all in the schoolhouse of sin, so that the promise would bring to graduation those who believe (v. 22). We were kept under the law until the faith (the promise) should be revealed (v. 23). The law was our paedogogue to bring us to Christ (v. 24). But once we have graduated and grown, the paedogogue is no longer needed (v. 25). So all, Jew and Gentile, are children of God through faith in Christ (v. 26). You do not need to be circumcised if you have been baptized; if you are baptized, you have put on Christ (v. 27). And this union in Christ creates true equality (v. 28). And you are Christ’s, you are also Abraham’s, and therefore an heir (v. 29).
So here is the point of the law. In historical theology, we often point to the three uses of the law. This distinction is quite helpful, as far as it goes. One use is to restrain evil men (1 Tim. 1:8-11). Another use is prepare the individual for salvation (Rom. 3:20; 5:20). And a third use is that of informing Christians what love actually looks like in action (Rom. 13: 8-10). But there is another important use of the law, a use that corresponds to preparing an individual for salvation. This is the role of preparing the world for salvation, and that is what we find here. Note that Paul is arguing that the law was given until the seed should come. He is not referring to the moment the seed “comes into the individual heart.” He is speaking of time when the seed comes into the world.
Then we have the puzzling phrase “God is one.” This passage is obscure, and it vexes the commentators greatly. After offering all appropriate qualifications, this is how I understand it. When we see Paul’s description of the law here, we see why he emphasizes that it was mediated. God was here and the sinful people to be redeemed were over there, and the law was mediated between them. But God is one, and does not need a mediating agent within Him. This meant that the Mosaic law did not rise to the status (so to speak) of a divine attribute. But our salvation is based on the very nature of God, and Paul has told us that this foundation is the promise. The promise does not need an external mediator. That promise is therefore contained within the triune life, and when we are united to Christ, we are united to that living promise.
If you are baptized, you have been baptized into Christ. Therefore, Paul argues, act like it. Now this is the hinge of the argument in Galatians. Why do Gentiles not need to be circumcised? They do not need to be circumcised because baptism marks them out as belonging to Christ. And if they are Christ’s, they are Abraham’s. And if they are Abraham’s, then they are heirs, and therefore do not need to be circumcised.
In Christ, all barriers to fellowship are dissolved. No longer is it possible to say that I can have nothing to do with you “because you belong to the wrong caste.” The three possible barriers to fellowship that Paul mentions here are racial and cultural, social, and sexual. And we may add more of our own—indeed, obedience requires it. We may not withhold fellowship based on income, race, manners, age, or Vietnam veteran era status. This should remind us; we do not object to the diversity crowd because they want to make bricks. We object to them because they want to make bricks without straw, and in some cases, without clay.