3:6 The Judaizers, in emphasizing the Mosaic Law, appealed to Moses frequently. Paul took them back farther in their history to Abraham, the father of the Jewish nation. He cited Genesis 15:6 to prove that God justified Abraham by faith, not because he kept the Law. Abraham believed the promise that God would bless him. Abraham could and did do nothing but believe God's promise that He would do something supernatural for him (cf. Rom 4:3).89His faith was his trust in God.
". . . Paul takes it for granted that Abraham's being justified by faith provesthat the Galatians must have received the Spirit by faith also; and this argument from Scripture falls to the ground unlessthe reception of the Spirit is in some sense equated with justification. For if this were not so, it could be objected that even though Abraham was indeed justified by faith, it does not necessarily follow that reception of the Spirit also has to be dependent on faith; conceivably while justification is by faith the gift of the Spirit could be conditioned on works. We may take it, then, that Paul conceives of receiving the Spirit in such close connection with justification that the two can be regarded in some sense as synonymous, so that in the Galatians' receiving the Spirit their justification was also involved."90
Genesis 15:6 is one of Paul's two key proof-texts for his teaching about justification by faith in Galatians (cf. Rom. 4:3). The other is Habakkuk 2:4, which he quoted in 3:11 (cf. Rom. 1:17).
This verse introduces Paul's major explanation of salvation history. It is a bridge concluding one section of his argument (3:1-6; "even so") and introducing the next (3:6-9; "Therefore,"v. 7).
3:7-9 "In this verse [v. 7] Paul extended his argument from Abraham to his posterity and raised for the first time the question that would dominate the remainder of Gal 3 and 4: Who are the true children of Abraham? This train of thought will find a conclusion in the allegory of the two mothers, Sarah and Hagar, and their two sons, Isaac and Ishmael (4:21-31)."91
The spiritualsons of Abraham, Paul contended, were not his physical descendants but those who believed God whether they were Jews or Gentiles. He expounded Genesis 12:3c and 22:18a (in the LXX) to prove his point. We should understand this promise to include salvation. Paul clarified that this is what God intended. However it is only those who trust God who enter into God's blessings for believers. Paul was not a universalist; he did not believe everyone will eventually go to heaven. Personal appropriation of God's gift is necessary for salvation.
The Judaizers were evidently teaching the Galatians that to become Abraham's children by adoption they had to receive circumcision. This was necessary for pagan proselytes to Judaism. They may have said that God had declared the Galatian Christians righteous by faith while uncircumcised like Abraham. Nevertheless now they needed to undergo circumcision as Abraham did. Circumcision would be a seal of their justification as it had been for Abraham. Circumcision would make them true sons of Abraham.
Paul argued that it was not circumcision that made a person a son of Abraham but faith. He treated circumcision as a part of the Law because even though God instituted it many generations before He gave the Law He reaffirmed it and incorporated it into the Law (Lev. 12:3).
"What endeared Abraham to many Jewish thinkers were his virtues and his deeds. They understood him to have kept the law before it was written."92
