The Galatians, being Gentiles, are just as much the children of God as believing Israelites. None are left under the jurisdiction or tutorship of the law.
Let us come to God as sons and daughters and make petitions to our loving heavenly Father. He does not want us to come as slaves but to have the confidence of beloved children as they approach their heavenly Father.
Doesn’t Scripture speak of the children of Israel as the people of God even while they were still under the covenant of the law, and doesn’t he promise to be their God? God calls the children of Israel ‘my people’ from the time that they begin to cry to him out of their oppression in Egypt (Exodus 3:7). This name is given to them because of their place in the Abrahamic covenant as the seed of Abraham, but although they are called the people of God, they are only God’s people in a limited sense, as a typical people, and God, because of their unregenerate conduct, denies that this temporary status entitles them to a permanent place in his house: ‘And Jehovah said, Call his name Lo-ammi; for ye are not my people, and I will not be your God’ (Hosea 1:9). But speaking of the international Jewish Gentile church Scripture says, ‘Yet the number of the children of Israel shall be as the sand of the sea, which cannot be measured nor numbered; and it shall come to pass that, in the place where it was said unto them, Ye are not my people, it shall be said unto them, Ye are the sons of the living God’ (Hosea 1:9). This tremendous benefit comes only through faith, because only through faith can we receive what we do not deserve, and the privilege of being the sons and daughters of God is one which we could never be worthy of.
Are not those who go to school children? And are they not children of the same father before they go to school and after they leave school? Yes, but Paul’s illustration requires an adoption into the family of God. For his point is that under the law the children of Israel were not children of God but slaves, not possessing liberty but bound to obey. When we believed in Christ, we became children of God by adoption, and therefore we cannot still be under the law or else we would still be called slaves.