21Tell me, you who desire to be subject to the law, will you not listen to the law? 22For it is written that Abraham had two sons, one by a slave woman and the other by a free woman. 23One, the child of the slave, was born according to the flesh; the other, the child of the free woman, was born through the promise.24Now this is an allegory: these women are two covenants. One woman, in fact, is Hagar, from Mount Sinai, bearing children for slavery. 25Now Hagar is Mount Sinai in Arabia and corresponds to the present Jerusalem, for she is in slavery with her children. 26But the other woman corresponds to the Jerusalem above; she is free, and she is our mother. 27For it is written, "Rejoice, you childless one, you who bear no children, burst into song and shout, you who endure no birthpangs; for the children of the desolate woman are more numerous than the children of the one who is married." 28Now you, my friends, are children of the promise, like Isaac. 29But just as at that time the child who was born according to the flesh persecuted the child who was born according to the Spirit, so it is now also. 30But what does the scripture say? "Drive out the slave and her child; for the child of the slave will not share the inheritance with the child of the free woman." 31So then, friends, we are children, not of the slave but of the free woman.
I very much like and appreciate how Dr. Chris Tilling [Tutor and Senior Lecturer in NT, St. Mellitus College, London] encapsulates Paul's overall teaching: the unconditional love of God revealed in Jesus Christ and in the Holy Spirit. This is the key for reading Paul.
Unfortunately an overemphasized reading of justification, as rendered by Martin Luther and other Protestant Reformers, has distorted Paul's own emphasis. From this particular Lutheran/Protestant angle, the problem of sin is guilt (i.e., the sinner stands guilty before a holy judge, God); and being guilty means you ought to be punished. Jesus' main contribution, then, is to take on our punishment. He dies in our stead. Receive Jesus in your heart so that you will be spared the punishment that was due you. That's the gospel according to Luther and others who followed his lead.
What about for the Apostle Paul?
For Paul, the main problem of sin is that it enslaves. Jesus sets us FREE. Sin --> Enslave --> Freedom!
The passage above clearly tracks with the twin notions of slavery and freedom. Hagar represents the Old Covenant of the Law, which enslaves; and Sarah represents the New Covenant of the Spirit, which frees. It's interesting how Paul interprets Hagar-Ishmael and Sarah-Isaac. The actual story of Old Covenant begins with Abraham/Sarah/Isaac. The Abraham/Hagar/Ishmael line within the Old Testament is never seen as part of the Old Covenant. However from Paul's New Covenant perspective, he can symbolically read into the old Hagar and Sarah stories as depicting the twin stories of the Old Covenant and the New.
The larger point, getting back to the big picture, is the importance of grasping what we are offered in Christ through the Spirit -- Freedom! (Later we will read Paul's emphatic words, "It is for freedom that Christ has set us free!" Gal. 5:1)
Freedom is the endgame. There are no other moves left on playing board. Freedom and all that is stored up of us in our freedom in Christ and in the Spirit. To go back to slavery after having experienced freedom is mind bogglingly foolish and dangerous from Paul's standpoint. Freedom is the great gift rendered by Christ on the cross. Let's enjoy our freedom today.
Let's pray: Father God, we thank you that Christ Jesus was sent by you, became incarnate and died on a cross, so that through the resurrection of Christ we might enter into the eschatological age of wholeness and freedom, no longer enslaved to sin and death. Help us to use our freedom to love you and love others and for us to grow in the Spirit. In Jesus' name, amen.