15 To give a human example, brothers: even with a man-made covenant, no one annuls it or adds to it once it has been ratified. 16 Now the promises were made to Abraham and to his offspring. It does not say, “And to offsprings,” referring to many, but referring to one, “And to your offspring,” who is Christ. 17 This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void. 18 For if the inheritance comes by the law, it no longer comes by promise; but God gave it to Abraham by a promise.
19 Why then the law? It was added because of transgressions, until the offspring should come to whom the promise had been made, and it was put in place through angels by an intermediary. 20 Now an intermediary implies more than one, but God is one.
21 Is the law then contrary to the promises of God? Certainly not! For if a law had been given that could give life, then righteousness would indeed be by the law. 22 But the Scripture imprisoned everything under sin, so that the promise by faith in Jesus Christ might be given to those who believe.
23 Now before faith came, we were held captive under the law, imprisoned until the coming faith would be revealed. 24 So then, the law was our guardian until Christ came, in order that we might be justified by faith. 25 But now that faith has come, we are no longer under a guardian, 26 for in Christ Jesus you are all sons of God, through faith. 27 For as many of you as were baptized into Christ have put on Christ. 28 There is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus. 29 And if you are Christ's, then you are Abraham's offspring, heirs according to promise.
4:1 I mean that the heir, as long as he is a child, is no different from a slave, though he is the owner of everything, 2 but he is under guardians and managers until the date set by his father. 3 In the same way we also, when we were children, were enslaved to the elementary principles of the world. 4 But when the fullness of time had come, God sent forth his Son, born of woman, born under the law, 5 to redeem those who were under the law, so that we might receive adoption as sons. 6 And because you are sons, God has sent the Spirit of his Son into our hearts, crying, “Abba! Father!” 7 So you are no longer a slave, but a son, and if a son, then an heir through God.
3 The Galatians were being lead to believe that their justification (being declared righteous) was based on their obedience to the law. But Paul points out that the father of faith, Abraham, was counted righteous 430 years before the law even came into existence. So the basis of his being declared righteous was not his obedience to the law but because he believed, trusted in God's promises.
Anticipating the conclusion of his opposers, Paul states their question: "Well then if righteousness comes--not by obedience to the law, but--by faith, why did God give the law?" It was added to reveal & reign in sin: to reveal the brokenness of humanity and its desperate need to be set free from its bondage, though unable to do anything about it but sin. Humanity had a problem no mere human could solve. Enter the God-man, Jesus the Christ!
4 Like a good baby sitter, the law kept the slaves-to-sin in check until the gift of faith brought the righteousness necessary to rebirth believers who received a new Govenor, One of love from the Father, through the Son: the Spirit of God. Believing slaves are reborn as sons, recipients of the promises fulfilled in God's Son, Christ Jesus the Lord.
What son measures his parentage by a birth cerificate? Isn't your Father's love greater to you than your last name? Yes, He made us: we are His. But we cry Abba, "daddy," because of the cross of Christ!