21 Tell me now, you who have become so enamored with the law: Have you paid close attention to that law? 22 Abraham, remember, had two sons: one by the slave woman and one by the free woman. 23 The son of the slave woman was born by human connivance; the son of the free woman was born by God's promise. 24 This illustrates the very thing we are dealing with now. The two births represent two ways of being in relationship with God. One is from Mount Sinai in Arabia. 25 It corresponds with what is now going on in Jerusalem - a slave life, producing slaves as offspring. This is the way of Hagar. 26 In contrast to that, there is an invisible Jerusalem, a free Jerusalem, and she is our mother - this is the way of Sarah. 27 Remember what Isaiah wrote: Rejoice, barren woman who bears no children, shout and cry out, woman who has no birth pangs, Because the children of the barren woman now surpass the children of the chosen woman.
Matthew Henry's Commentary on Galatians 4:21-27
Commentary on Galatians 4:21-27
(Read Galatians 4:21-27)
The difference between believers who rested in Christ only, and those who trusted in the law, is explained by the histories of Isaac and Ishmael. These things are an allegory, wherein, beside the literal and historical sense of the words, the Spirit of God points out something further. Hagar and Sarah were apt emblems of the two different dispensations of the covenant. The heavenly Jerusalem, the true church from above, represented by Sarah, is in a state of freedom, and is the mother of all believers, who are born of the Holy Spirit. They were by regeneration and true faith, made a part of the true seed of Abraham, according to the promise made to him.