“Brothers and sisters: It is written that Abraham had two sons, one by the slave woman and the other by the freeborn woman. The son of the slave woman was born naturally, the son of the freeborn through a promise. Now this is an allegory. These women represent two covenants. One was from Mount Sinai, bearing children for slavery; this is Hagar. But the Jerusalem above is freeborn, and she is our mother. For it is written: Rejoice, you barren one who bore no children; break forth and shout, you who were not in labor; for more numerous are the children of the deserted one than of her who has a husband. Therefore, brothers and sisters, we are children not of the slave woman but of the freeborn woman. For freedom Christ set us free; so stand firm and do not submit again to the yoke of slavery.” Galatians 4:22-5:
A very important clue is given by St. Paul, he states, "brothers and sisters, we are children not of the slave woman but of the freeborn woman." I ask again, who is this freeborn woman? For Christians, this could only be one woman. It is the same woman of Revelation 12:17, "Then the dragon was angry with the woman, and went off to make war on the rest of her offspring, on those who keep the commandments of God and bear testimony to Jesus." It is the same woman of John 19:26, When Jesus saw his mother, and the disciple whom he loved standing near, he said to his mother, "Woman, behold, your son!"
The idea of freeborn woman would also point to the woman of the Immaculate Conception! There is only one freeborn woman and that is Mother Mary.