10 For all who rely on works of the law are under a curse; for it is written, “Cursed be everyone who does not abide by all things written in the Book of the Law, and do them.” 11 Now it is evident that no one is justified before God by the law, for “The righteous shall live by faith.” 12 But the law is not of faith, rather “The one who does them shall live by them.” 13 Christ redeemed us from the curse of the law by becoming a curse for us—for it is written, “Cursed is everyone who is hanged on a tree”— 14 so that in Christ Jesus the blessing of Abraham might come to the Gentiles, so that we might receive the promised Spirit through faith.
Cole, in the Tyndale Commentary, sums up Paul's argument in these words: 'Why talk about Abraham when the real question is the law? Abraham stood at the very beginning of God's revelatory process. Centuries later God crowned the process by giving the law of Moses. It is by keeping this law that Israel looks for salvation. If God in His mercy used some other system with Abraham, that was because there was as yet no law to keep.... To them all this talk about Abraham was irrelevant to the main issue'. It is this that Paul decisively denies in the argument of these verses, the thread of which may be summarised as follows: (i) the way of salvation is by faith, not by the works of the law; (ii) the way of salvation by faith has always been the way, and it goes right back to Abraham's time; (iii) the way of salvation by faith, going right back to Abraham's time, is not in any way affected by the giving of the law. The law was a later addition, and could not have affected the promise, which was unalterably fixed, by covenant and blood. Redemption, in fact, has to be by promise and by grace, since the law cannot redeem. And Christ has stepped in, and stood in for us, to redeem us from the curse of the law and its condemnation, that we might have the promise of the Spirit, i.e. the gift of justification and eternal life. But in Christ becoming a curse for us, something real took place. A real bondage had to be broken, and a real price had to be paid. This is the meaning of the word 'redeem' - it means to set free by the payment of a price. That price was the condemnation and curse of God upon sin, and in paying it Christ endured in Himself the condemnation of divine wrath upon Himself.