Commentary - Galatians 4:21-31

Bird's-eye view

In this section of Galatians, Paul brings his argument against the Judaizers to a sharp and decisive point. He has been arguing that salvation is by grace through faith, entirely apart from works of the law. Now, to drive the point home, he uses an allegory drawn from the very law his opponents are so keen on. He takes the story of Abraham's two sons, Ishmael and Isaac, and shows how they represent two covenants, two ways of relating to God. This is not just a clever debater's trick; it is a profound theological argument rooted in redemptive history. Paul is showing the Galatians that their desire to go back under the law is not a step toward maturity, but a regression into slavery. It is to choose the line of Hagar and Ishmael over the line of Sarah and Isaac. The choice is between bondage and freedom, between the flesh and the Spirit, between the earthly Jerusalem that is in slavery and the heavenly Jerusalem which is free, and is our mother.

The core of the argument is this: the Judaizers, who claim to be the true heirs of Abraham, are in fact acting like Ishmaelites. They are persecuting the true children of promise, just as Ishmael persecuted Isaac. By seeking righteousness through their own efforts, they are aligning themselves with the covenant of works, represented by Hagar and Mount Sinai. But believers in Christ, Paul argues, are children of the promise, born of the Spirit, just like Isaac. Our standing with God is not based on our pedigree or our performance, but on God's sovereign promise, received by faith. The passage concludes with a radical application: the slave woman and her son must be cast out. This is not a call for personal animosity, but a demand for theological and ecclesiastical purity. The gospel of grace cannot coexist with the gospel of works. One must give way to the other. We are children of the free woman, and we must live like it.

Outline

Clause-by-Clause Commentary

v. 21 Tell me, you who want to be under law, do you not listen to the Law?

Paul begins with a direct, almost confrontational, question. He is addressing those in the Galatian churches who have been swayed by the Judaizers and are now desiring to place themselves under the Mosaic Law. His question is dripping with a holy irony. "You want to live by the law? Fine. Let's open it up. Are you actually paying attention to what it says?" The Judaizers were using the law to bind men's consciences, but Paul is about to use the very same law to set them free. He is demonstrating that his opponents don't truly understand the Torah they profess to champion. They read it as a rulebook for earning salvation, a ladder to climb up to God. Paul reads it as God's story of redemption, a story that points away from self-effort and toward God's sovereign promise.

v. 22-23 For it is written that Abraham had two sons, one by the servant-woman and one by the free woman. But the son by the servant-woman had been born according to the flesh, while the son by the free woman through the promise.

Here Paul lays the historical foundation for his allegory. He goes back to Genesis, to the patriarch Abraham, whom the Judaizers revered. The facts are simple and undisputed. Abraham had two sons: Ishmael by Hagar, Sarah's Egyptian slave, and Isaac by Sarah, his free wife. The crucial distinction, however, lies not in their parentage alone, but in the manner of their births. Ishmael was born "according to the flesh." This was man's plan. This was Abraham and Sarah trying to "help God out." It was a work of human ingenuity, a product of natural processes, a result of trying to secure the promise by their own strength. Isaac, on the other hand, was born "through the promise." His birth was a flat-out miracle. It was contrary to nature, contrary to all human expectation. Sarah was barren and well past the age of childbearing. Isaac's existence was a testimony not to Abraham's virility, but to God's fidelity. He was a child of pure grace.

v. 24-25 This is spoken with allegory, for these women are two covenants: one from Mount Sinai bearing children into slavery; she is Hagar. Now this Hagar is Mount Sinai in Arabia and corresponds to the present Jerusalem, for she is in slavery with her children.

Now Paul springs the trap. He says this historical account is an allegory. He is not saying the story isn't historically true. He is saying that God embedded a deeper, typological meaning within the historical facts. The two women, Hagar and Sarah, represent two covenants. Hagar, the slave woman, represents the covenant made at Mount Sinai. This is a stunning move. The Judaizers gloried in the Sinai covenant, but Paul labels it a covenant that "bears children into slavery." Why? Because when the law is approached as a means of justification, it can do nothing but condemn. It reveals sin and pronounces a curse on all who fail to keep it perfectly. It becomes a taskmaster, and those who live under it are slaves to its demands, slaves to fear, and ultimately slaves to sin and death. Paul then connects Hagar directly to "the present Jerusalem," the center of first-century Judaism that had rejected its Messiah. That Jerusalem, with its temple and its rituals, was in bondage to a works-righteousness system, and her children were enslaved with her.

v. 26 But the Jerusalem above is free; she is our mother.

In stark contrast to the earthly Jerusalem stands "the Jerusalem above." This is the heavenly city, the true church of God, the assembly of the firstborn enrolled in heaven. She is not bound by earthly strictures or ethnic qualifications. She is free. And this free city, this heavenly reality, is "our mother." Believers are not children of the earthly institution centered in unbelieving Israel. We are citizens of heaven. Our identity is not derived from a physical place or a legal code, but from a spiritual reality established by God in Christ. Our mother is the covenant of grace, the realm of freedom purchased by Christ.

v. 27 For it is written, “REJOICE, BARREN WOMAN WHO DOES NOT GIVE BIRTH; BREAK FORTH AND SHOUT, YOU WHO ARE NOT IN LABOR; FOR MORE NUMEROUS ARE THE CHILDREN OF THE DESOLATE ONE THAN OF THE ONE WHO HAS A HUSBAND.”

To support his point, Paul quotes from Isaiah 54:1. In its original context, this was a promise to exiled Israel, who felt barren and desolate. But Paul applies it to Sarah, the barren woman who miraculously gave birth, and by extension, to the church, the Jerusalem above. The point is that God's work is most gloriously displayed in situations of human impossibility. The "barren woman" (Sarah, the church of the Gentiles) will ultimately have more children than the one who "has a husband" (Hagar, ethnic Israel trusting in her covenant status). God's family is not built by natural generation but by supernatural regeneration. The gospel goes out and creates children of God from the barren nations of the world, far outnumbering those who could claim a physical descent from Abraham.

v. 28 And you brothers, in accordance with Isaac, are children of promise.

Paul now makes the application personal and direct. "You brothers", these Gentile believers in Galatia, "are children of promise." Your spiritual lineage is not traced back to Sinai, but to the promise God made to Abraham, a promise fulfilled in Christ. Like Isaac, your spiritual birth is a miracle of God's grace. It didn't happen because you were circumcised or because you kept the kosher laws. It happened because God promised it and God performed it. You are heirs of the same grace that brought Isaac into the world.

v. 29 But as at that time he who was born according to the flesh was persecuting him who was born according to the Spirit, so it is now also.

History repeats itself, or rather, the underlying spiritual conflict remains the same. Paul alludes to Genesis 21:9, where Ishmael was "mocking" or "playing with" Isaac in a scornful way, which Sarah saw as a threat. Paul interprets this as persecution. The son of the flesh will always be hostile to the son of the promise. The religion of human achievement will always resent the religion of divine grace. And so, Paul says, it is now. The Judaizers, the spiritual sons of Hagar, are persecuting the Galatian believers, the spiritual sons of Sarah. This persecution is a confirmation of their true spiritual identity. The children of the flesh harry the children of the Spirit.

v. 30 But what does the Scripture say? “CAST OUT THE SERVANT-WOMAN AND HER SON, FOR THE SON OF THE SERVANT-WOMAN SHALL NOT BE AN HEIR WITH THE SON OF THE FREE WOMAN.”

If the diagnosis is correct, what is the prescription? Paul turns again to Scripture, quoting God's command to Abraham from Genesis 21:12. The solution is not compromise or integration. It is expulsion. "Cast out the servant-woman and her son." There can be no shared inheritance. The son of slavery cannot be co-heir with the son of freedom. The teaching of the Judaizers, this gospel of works, has no place in the household of faith. It must be driven out. Paul is not advocating for personal cruelty, but for doctrinal purity. The two systems are mutually exclusive. To mix law and grace is to corrupt the gospel and to forfeit the inheritance.

v. 31 So then, brothers, we are not children of a servant-woman, but of the free woman.

Paul concludes with a triumphant declaration that summarizes the entire argument. The choice has been laid bare. On one side is Hagar, Sinai, slavery, the flesh, the earthly Jerusalem, and persecution. On the other is Sarah, promise, freedom, the Spirit, the heavenly Jerusalem, and the inheritance. The Galatians must choose their mother. And Paul, speaking for himself and all true believers, makes his own position unequivocally clear. We are not children of Hagar. We do not belong to the covenant of works. We are children of Sarah, the free woman. Our identity, our inheritance, and our entire way of life are defined by the glorious liberty of the children of God.