We were under the law until Christ came, as the heir is under the guardian until he is of age, 1-4. But Christ freed us from the law, 5, 6; therefore we are servants no longer to it, 7-13. Paul remembers their good will to him and his to them, 14-21; and shows that we are the sons of Abraham by the free-woman, 22-31.
1 Now I say, that the heir, as long as he is a child, differs nothing from a servant, though he is lord of all, 2 But is under guardians and governors until the time appointed by the father. 3 Even so we, when we were children, were in bondage under the elements of the world. 4 But when the fullness of the time had come, God sent forth his Son, born of a woman, born under the law, 5 To redeem those who were under the law so that we might receive the adoption of sons. 6 And because you are sons, God has sent forth the Spirit of his Son into your hearts, crying, "Abba, Father." 7 Therefore, you are no longer a servant, but a son, and if a son, then an heir of God through Christ.
8 However then, when you did not know God, you did service to them which by nature are not gods. 9 But now, after you have known God, or rather are known by God, how do you turn back to the weak and beggarly elements to which you desire again to be in bondage? 10 You observe days, months, times, and years. 11 I am afraid for you, lest I have bestowed upon you labor in vain.
12 Brothers, I implore you, be as I am, for I am as you are. You have not injured me at all. 13 You know that in infirmity of the flesh I preached the gospel to you at the first. 14 And that which was a trial to you in my flesh you did not despise, nor reject, but received me as an angel of God, even as Christ Jesus. 15 What then was the blessedness you spoke of? For I bear you testimony, that if it had been possible, you would have plucked out your own eyes and given them to me. 16 Have I therefore become your enemy because I tell you the truth? 17 They zealously affect you, but not in a good way, but they wish to exclude you so that you may be zealous for them. 18 But it is good to be zealously affected always in a good thing, and not only when I am present with you. 19 My little children, of whom I travail in birth again until Christ is formed in you, 20 I desire to be present with you now and to change my voice, for I stand in doubt of you.
21 Tell me, you who desire to be under the law, do you not hear the law? 22 For it is written that Abraham had two sons: one by a woman-servant, the other by a free-woman. 23 But he who was of the woman-servant was born according to the flesh, but he of the free-woman was by promise. 24 These things are an allegory, for these are the two covenants. One is from the mount Sinai, bearing children to bondage, which is Hagar. 25 For this Hagar is mount Sinai in Arabia, and answers to Jerusalem which now is, and is in bondage with her children. 26 But Jerusalem which is above is free, and she is the mother of us all. 27 For it is written,
"Rejoice, you barren who do not bear./
Break forth and cry, you who do not travail./
For the desolate has many more children/
than she who has a husband."
28 Now we, brothers, as Isaac was, are the children of promise. 29 But as then he who was born according to the flesh persecuted him who was born according to the Spirit, even so it is now.
30 Nevertheless, what does the Scripture say? "Cast out the woman-servant and her son. For the son of the woman-servant shall not be heir with the son of the free-woman."
31 So then, brothers, we are not children of the woman-servant, but of the free.
Matthew Henry Commentary - Galatians, Chapter 4[➚]
[v.6] - "Abba" - Definition: "Father," also used as the term of tender endearment by a beloved child – i.e. in an affectionate, dependent relationship with their father; "daddy," "papa."
[v.22a] - "one by a bond-maid" - Reference, Genesis 16:15.
[v.22b] - "the other by a free-woman" - Reference, Genesis 21:2.
[v.27] - Quoting Isaiah 54:1 (LXX).
[v.29] - Reference, Genesis 21:9.
[v.30] - Quoting Genesis 21:10 (LXX—paraphrased).