Paul told the Galatians if they wanted to be under the law, they must not have heard the part he’s about to describe (v. 21). God promised Abram a son, but his wife was barren (Gen.11:30), so when God said he’d have a “seed” (12:3) he knew God planned to miraculously give him one. But he impatiently had a son by his servant (Gen.16:1-4cf.Gal.4:22).
Hagar’s son was born “after the flesh” (v.23), after “the will of the flesh” (cf.Jo.1:13).It was God’s will Abraham wait for Sarah’s son, but it was the will of his flesh to father Ishmael. This is an “allegory” (4:24), an illustration. They’re used for kids, but the Galatians were acting like “children” (4:19).
Hagar represented “mount Sinai” (v.25), i.e., the “covenant” of the law (Deut.33:2) that God gave Israel when He gave them 613 commandments, and said He’d give them eternal life if they could keep them all perfectly! They couldn’t, so it “gendereth to bondage” (v.24), i.e., it sired (cf.Job 21:10) slaves who had to be told “thou shalt” and “thou shalt not.”
Hagar “answereth to” Jerusalem (Gal.4:25), i.e., she looked like Jerusalem (cf.Pr.27:19). That is, you could see Jerusalem in her story. Abraham and Sarah told her “thou shalt” etc. “All her children” were also slaves (4:25) because the child of a slave is a slave, and the people of Jerusalem were enslaved from Day One. They became God’s people the day Moses gave them the law (Deut.27:1,9), and the people they became were bondslaves. And all her children were slaves because the son of a slave is a slave.
But Sarah represented the Jerusalem in heaven (Gal.4:26 cf. Heb.12:22) that will be on the earth (Rev.21:2) as opposed to the Jerusalem “which now is.” Her kids are “free” because the children of free women are free. Her kids are saved Jews under the law, but Paul reveals she is the mother of “all” Gentile believers too, just as Abraham is our father (Rom.
4:16). We are “free” from the bondage of sin (Jo.8:33,34).
Paul says Hagar had a husband (Gal.4:27) because she is said to be Abraham’s “wife” (Gen.16:3). She represented Jerusalem under the law, whose husband was God (Jer.2:2). He married her with wedding vows (Deut.26:17,18). Sarah did not have a husband, because she represents Jerusalem above, who won’t have a husband until Revelation 20:7; 21:9,10.
That explains why Galatians 4:27 says Sarah had more kids than Hagar. There have never been more Jews than Arabs, but in New Jerusalem, there’ll be more saved Jews than there ever were Arabs. Paul was quoting Isaiah 54:1, and as a prophet, Isaiah was predicting Sarah would have more kids in God’s eternal kingdom (54:1-13). In that kingdom, saved Jews will continue to have kids (Isa.9:7) and complete God’s plan to populate heaven and earth, a plan Adam interrupted.
There’s no need to join legalizers to be in the majority now.
Paul mentions this to comfort the Galatians. They were in the minority compared to unsaved Jews, but someday they’ll be the majority, and us with them! We’re Abraham’s legitimate seed (Gal.4:28). God promised Abraham a legit son by a miraculous birth, and our spiritual birth is just as miraculous, and just as apart from “the will of the flesh” (Jo.1:13).
But along with the blessing of being Abraham’s legitimate children like Isaac was, we inherit a problem he had. Abraham’s unsaved son persecuted his saved son (Gal.4:29), because God said he couldn’t have part of Isaac’s inheritance (Gal.4:30). Unbelievers still persecute believers (II Thes. 2:14,15) because they don’t get any part of our inheritance. Mocking (Gen.21:9) is about all the persecution we get, but all who live godly in Christ will receive it (IITim.3:12).
Paul closes this passage by assuring the Galatians that those unsaved Jews will be cast out (4:30), then assures them that they won’t be part of those who are cast out (v.31). Us either!