Galatians 4:21 - 5:1
21 Tell me, you who want to be under law, do you not listen to the Law?
22 For it is written that Abraham had two sons, one by the servant-woman and one by the free woman.
23 But the son by the servant-woman had been born according to the flesh, while the son by the free woman through the promise.
24 This is spoken with allegory, for these women are two covenants: one from Mount Sinai bearing children into slavery; she is Hagar.
25 Now this Hagar is Mount Sinai in Arabia and corresponds to the present Jerusalem, for she is in slavery with her children.
26 But the Jerusalem above is free; she is our mother.
27 For it is written, “Rejoice, barren woman who does not give birth; Break forth and shout, you who are not in labor; For more numerous are the children of the desolate one Than of the one who has a husband.”
28 And you brothers, in accordance with Isaac, are children of promise.
29 But as at that time he who was born according to the flesh was persecuting him who was born according to the Spirit, so it is now also.
30 But what does the Scripture say? “Cast out the servant‑woman and her son, For the son of the servant‑woman shall not be an heir with the son of the free woman.”
31 So then, brothers, we are not children of a servant-woman, but of the free woman.
5:1 It was for freedom that Christ set us free. Therefore, stand firm and do not be subject again to a yoke of slavery.
"If we are Christians, we are like Isaac, not Ishmael. Our descent from Abraham is spiritual not physical. We are not his sons by nature, but by super-nature.” (John R. W. Stott)
“Those who try to achieve the status of sons and heirs by the righteousness of the Law or by their own righteousness are slaves, who will never receive the inheritance even though they work themselves to death with their great effort; for they are trying, contrary to the will of God, to achieve by their own works what God wants to grant to believers by sheer grace for Christ’s sake.” (Martin Luther)