Which is more important, the unity of the church or its purity? To which are we to give preference: love or truth, fellowship or doctrine? The apostle Paul places great emphasis on unity: “Now you, brothers, like Isaac, are children of promise” (Gal. 4:28). Galatian Gentiles and all believers are “brothers,” are “like Isaac,” and, as such, are “children of promise.” We are all spiritual children of Abraham and Sarah. We have become “children of promise,” descendants of Abraham “like Isaac,” not through birth, but rebirth; not by law, but by promise; not by works, but by faith. “If you are Christ’s,” Paul wrote, “then you are Abraham’s offspring, heirs according to promise” (Gal. 3:29).
This is a great promise, but there is a catch. Wonderful as it is to be “like Isaac,” a “child of promise,” there is a downside. If we are “like Isaac,” then we can expect to be treated like Isaac by the unbelieving. “But just as at that time he who was born according to the flesh persecuted him who was born according to the Spirit, so also it is now” (Gal. 4:29).
The apostle Paul doesn’t take the believers’ identification with Isaac where we might have expected him to go. We might have expected him to speak of the blessings of the covenant, or elaborate upon the gifts and privileges of salvation. Instead, being “like Isaac” means persecution. The one born “according to the flesh persecuted him who was born according to the Spirit.” The apostle is referring to the “mocking” of Isaac by Ishmael recorded in Genesis 21:9. Ishmael was “born of the flesh,” that is, through human devising, whereas Isaac was “born according to the Spirit.” This mocking by Ishmael of Isaac corresponds to the persecution of believers who profess to know God but are ensnared in legalism. Remember, Ishmael was circumcised, a member (by analogy) of the visible church. “So also it is now,” Paul says. This explains why in the early years of the church Judaism persecuted Christianity and why so often the persecution of the church arises from within the church. Christians are often persecuted “by their half-brothers — the unbelieving but religious people in the nominal church,” says James Montgomery Boice.
I can only think of one time in twenty years that our congregation has suffered persecution, either fierce or mild, from outside the organized church. But from within? I can hardly think of anything good that hasn’t been resisted, often fiercely, by those who do not understand the gospel, whether from the legalistic end of the spectrum or the libertine. On a personal level, Christian people typically suffer far more at the hands of fellow professing Christians than people of the world. Think of your own wounds and scars of recent years. Who has inflicted them? Who has discouraged and defeated you? Has not most of this come to you from within the visible church? Why? Because the besetting sin of zealous Christians is Pharisaic self-righteousness. We can become Pharisees about food and drink, child-rearing and education, fashion and finances, and make these tests of orthodoxy.
Consequently, being “like Isaac” means separation. What should be done about this conflict between law and grace? The apostle Paul cites the precedent of Genesis 21:10 in which Hagar and Ishmael are “cast out” and not given an inheritance with Isaac. His meaning is clear: both legalism and the legalists are to be excluded from the church.
But what does the Scripture say? “Cast out the slave woman and her son, for the son of the slave woman shall not inherit with the son of the free woman” (Gal. 4:30).
Finally, there must be a separation for those who destroy the graciousness of the gospel with their religion of works-righteousness. The persecutor of the church from within cannot be allowed to continue forever. There must be relief, and though “cast out” doesn’t sound very nice, there comes a point where vigorous action must be taken. A few years back we had a member of our church regularly mailing out to other members attacks aimed at the leadership of the church and the gospel as we were preaching it. The mailings were tolerated for a while. But they were keeping the church in a state of turmoil. Action was necessary and rightly taken by the elders.
“So,” he says. “My point has been made,” he means in effect. We are children of Sarah, “the free woman” (v. 31). The proof? We are “like Isaac.” We are persecuted by those in bondage to the law and works; and we, like he, must separate from the legalists so as to protect the gospel.
This is not a happy task that the apostle Paul assigns but a necessary one. Lose the gospel and you lose the church, never mind its fellowship and unity. Though feelings may be hurt, though the people of this world may misunderstand, the bondwoman and her son must be cast out. At all costs, the gospel in its purity must be preserved.