This scripture is an illustration of the two covenants: Hagar the type of one, Sarah the other; the child of Hagar the type of those who are brought into the nominal fold of Christ through human scheming, the child of Sarah a type of those who are brought in solely through the promise and power of the Lord Jesus Christ. Hagar bore children to bondage, for she was a bondmaid. So all those who are endeavoring to save themselves by any scheme of man are in bondage. They never can break their bondage themselves; and all they can save, or convert, to such a system are also children of bondage. On the other hand, Sarah was a freewoman, and her children were free, and she therefore represents God's order; and all those who are saved through the Lord Jesus Christ by faith are the children of Sarah and the children of Abraham, children of freedom. The two things are represented by earthly Jerusalem and heavenly Jerusalem. The Jerusalem of the earth is in bondage with her children, and was then. She rejected God and followed her own way. The Jerusalem which is above is free. She was created and exists by the promise of God. She is therefore called the mother of the children of faith. Isa. 54:1 is quoted to prove this. The apostle concludes, therefore, that those who believe are just as Isaac was, children of promise. And then, too, as Ishmael persecuted Isaac, so those who are the children of bondage persecute those who are free in Christ Jesus. Those who follow the schemes of men will use the schemes of men to suppress what they think to be error, but in the glorious outcome God will save His children. It is better to be the children of freedom in Christ, tho in bondage here, than to be the children of sin-bondage, tho they may for a while seem to be in power.