We have seen that the “seed” of Galatians 3:16 is referring to Genesis 17:8. In Galatians 3:16, Paul is explaining to the gentile Galatians that the “seed” of Genesis 17:8 is the “one” nation Israel, not the “multitude” of nations who will also have Abraham as their father (Genesis 17:5).
In Galatians 3:17, Paul goes on to explain that the covenant has already been ratified. When was this covenant to Abraham and his seed “ratified by God” and thus made inviolable (3:17)?
(This post is part of a series)
As we have seen in our survey of the Old Testament, a solemn oath or ceremonial act is needed to make a covenantal relationship of obligation legally binding. The covenant of land in Genesis 15 was ratified by the events recorded in the chapter—the passing of the flaming torch through the pieces, followed by solemn promises. But it is only after the Aqedah (binding) of Isaac that God finally makes a solemn oath that “in your seed shall all the nations of the earth be blessed, because you have obeyed my voice” (Gen 22:16–18). Almost paradoxically, the primary act of loyal devotion that made Abraham and his seed a fitting covenant partner with God—a fitting agent for blessing to the whole world—was the willingness of Abraham to sacrifice the seed himself. It is only when the seed is placed on the wood and a sacrifice is made that God ratifies his covenant, emphatically vowing to make Abraham’s seed numerous and victorious (Gen 22:17) and thereby to bless the world through Abraham’s seed (22:18). Hahn presents a strong case that this is the “ratification” Paul has in mind, and that the Aqedah is the type for his exposition of Jesus’ crucifixion and the subsequent blessing to the nations in Galatians 3:13–14. In Genesis, the covenant of international blessing is ratified after Abraham’s supreme act of loyalty in being willing to sacrifice the “seed” of the promise by binding him “upon wood”:
Thus, the sense of [Galatians 3:]13–14 is that the death of Christ ἐπὶ ξύλου allows the blessing of Abraham after the Aqedah (Gen 22:18) to flow to the ἔθνη through Jesus Christ (ἐν Χριστῷ Ἰησοῦ).
Hence it is “Christ” who is supremely the seed, the one in whom all nations are blessed (Gal 3:16). This accords with the flow of biblical thought. Psalm 72 focusses the international scope of the promise to Abraham and his “seed” directly onto an ideal Davidic ruler (cf. 2 Sam 7). It is this Messiah-king “in whom all the nations will be blessed / bless themselves” (Psa 72:17, cf. Gen 12:3, 22:18). Christ is the seed who fulfils the covenantal oath that God swore to Abraham by his obedience to death on the cross.
The larger import of this for Paul’s argument with his opponents is that the covenantal obligations laid upon Abraham (circumcision) and his national seed (the law) as a prerequisite for international blessing are not laid upon the nations as a prerequisite for their own blessing. Abraham’s seed has fulfilled the covenantal obligations. The multitude of nations, therefore, are not called to enter this covenant, but to find blessing in the “seed”, to be “immersed” into Christ, to be “clothed” with Christ (Gal 3:27). This comes about by the Spirit and by faith in Christ (Gal 3:14). The blessings include justification (Gal 3:24), sonship (Gal 3:27) and unity with God and others in Christ (Gal 3:28). Hence it is faith in Christ, not covenant membership, that makes the Gentiles “seed of Abraham, heirs according to the promise” (Gal 3:29). Being the “seed of Abraham” does not mean that the Gentiles are subject to the covenantal obligations, for these obligations have been fulfilled by Christ’s sacrifice. Rather, being the “seed of Abraham” means that the Gentiles are now sons of God in the fullest sense, heirs of the inheritance that has now come in Christ (Gal 4:1–7). Even the Jews who were members of the covenant must also be in the “seed” by faith (Gal 2:16, 3:11). Hence Abraham’s international fatherhood is not by means of common covenantal membership, but by means of a common faith in the God who achieves his astounding promises (Gal 3:7, 9), and a common blessing of righteousness; the characteristics that Abraham had before any of the covenants was made (Gal 3:6, Gen 15:6).
 Williamson, Abraham, 246–48.
 Hahn, “Covenant, Oath, and the Aqedah”, 90–94.
 Hahn, “Covenant, Oath, and the Aqedah”, 93.
 Hahn, “Covenant, Oath, and the Aqedah”, 96–97.
 Williamson, Abraham, 167–70.
 If this were so, then Carol K. Stockhausen, “2 Corinthians 3 and the Principles of Pauline Exegesis”, in Paul and the Scriptures of Israel (ed. Craig A. Evans and James A. Sanders; Journal for the Study of the New Testament Supplement Series 83; Sheffield: JSOT, 1993), 143–64 (esp. 158–61) would be correct in concluding that Paul saw a real contradiction between the unilateral covenant of Genesis 15 and the bilateral covenant of Genesis 17.