Now you, brothers, like Isaac, are children of promise. But just as then the child born according to the flesh persecuted the one born according to the Spirit, so also now. But what does the Scripture say? Drive out the slave and her son, for the son of the slave will never be a coheir with the son of the free woman.
In the Book of Galatians, Paul uses the historical narrative of Abraham, Sarah, Hagar, and their children as an illustration. Those who trust their own efforts, their own merits, are like Ishmael—children conceived in slavery. Those who are His are like Isaac—children of promise. We are His not because of anything we have done, not because of our impulses, our desire, our efforts, or our merits. We belong to Him only because of His grace.
Because we are His, we can expect persecution. In fact, anyone who wants to live a godly life in Christ Jesus will be persecuted. And this persecution often comes from the religious.
In the Galatian churches, legalists were persecuting and troubling the believers. They were burdening them with instructions to supplement the grace of Christ with circumcision and the law. Just as Ishmael mocked Isaac (Genesis 21:9), legalists were giving commands, barking orders, and playing the role of religious rule-makers and religious police. Of this passage, John Stott wrote:
“We must expect the same. The persecution of the true church, of Christian believers who trace their spiritual descent from Abraham, is not always by the world, who are strangers unrelated to us, but by our half-brothers, religious people, the nominal church. It has always been so.”
Legalists will always mock and persecute those in awe of God’s grace. Legalists don’t really like grace, though they insist they do, because grace reminds us that we have done absolutely nothing to qualify ourselves to stand before God. Grace strips the legalist of his ability to hold others to the standard he believes he has lived up to.
The legalist, not the beggar aware of his need for grace, hurts the community of faith. According to Paul, it is the legalist, not the beggar, who needs to be driven out.