INTRODUCTION: Keep in mind that Paul's use of the term “heir” and “sons” is related to the great promise of redemption (justification) made to Abraham. The son, meaning the heir, inherits the promised blessing. In the preceding section (3:23-29), Paul argued that whether we are Jews or Gentiles we become sons of Abraham and consequently heirs of the redemptive promise by faith in Christ. Son ship is not thus determined by flesh but by faith in the Lord. This terminology and line of reasoning are continued in this new section. Herein it is Paul's purpose to illustrate how these Galatian Gentiles though made free from bondage (slavery) to sin can nevertheless by going under the law of Moses go back to the bondage of sin. He illustrates this by showing the bondage of the Jews while under the law, and thus the certainty of bondage for any who would choose to go under it.
I. JEWS UNDER LAW IN BONDAGE TO SIN, 4:1-3.
A. CHILDREN, LIKE SLAVES, HELD IN BONDAGE, 1-3.
Jews under the law were like children who were too young to inherit their father's estate, and therefore, though heirs were no closer to the inheritance than slaves (bond-servants) in their father's household. “Rudiments of the world” --The word's rudiments actually refer to the ABC'S of knowledge. It is the first branch of learning. Any rudimentary is elementary, for children, not adults. The point seems to be that the ordinances of the law of Moses were unable to bring those under it to salvation. The law could not make full grown sons out of its children.
B. THE PURPOSE FOR CHRIST'S COMING IN THE FULNESS OF TIME, 4-7.
It was to redeem those under the law (v. 5). The proof of this act of redemption was the Apostolic miracles witnessed by both Jew and Gentile (3:5). God sent forth His to your hearts crying “Abba Father.” Poof that Gentiles now inherit salvation and becomes 'sons.'
C. AN HEIR THOROUGH GOD, 7.
This is properly a conclusion to the foregoing. We are heirs, that is full grown sons, not by what the law did, but by what God did through Christ. CF Rom. 8:1-3.
II. GENTILES UNDER LAW IN BONDAGE TO SINS, 4:8-11.
Paul's reason for telling these Gentiles about Jews being in bondage while under law as to show that anyone else who was under law would be in the same condemnation.
A. IN BONDAGE UNDER IDOLATRY, 8.
“ At that time” when in idolatry.
“ No gods,” idols. By their very nature being fashioned from wood or stone or metal idols are not gods.
The Galatians were freed from bondage when thorough Paul's preaching they “came” to know God.
B. RETURNED TO BONDAGE BY GOING UNDER THE LAW, 9-11.
Paul shows that the law is no better than idolatry to make us free from sin.
1. “Weak and beggarly rudiments. “ The ordinances of the law were too impotent to free from sin. They were merely “carnal ordinances” imposed until the fullness of time when they would be replaced by the system of faith, See Heb. 9: 10; 10: 1-4.
2. Observances of Jewish ritual “In Vain.” No observance of the law's ordinances, however sincere, is able to bring one out from under the bondage of the law. The days, months, seasons and years of Judaism, like circumcision and sabbath keeping, are vain, being merely weak and beggarly ordinances without power to remove sin.
CONCLUSION: The law of Moses, as a legal system imposing mere carnal ordinances never designed by God to free men's conscience from sin (Heb. 10th chapter), thus a short falling in the law. Any and all efforts to return to the law are declared by the apostle to be “in vain.”