This is the beginning of my intermittent and ongoing examination of Paul's breakdown of law, faith, obedience and grace.
In Galatians, Paul looks at God’s covenant with Abraham not as something that was ever intended to operate in the literal, common sense understanding as it was presented to Abraham in Genesis but as a covenant that contained encoded elements would be refracted into different applications in the course of redemptive history. In Galatians, Paul makes interpretive leaps in regard to the symbolism covenant of God with Abraham as they apply to the Gospel: Paul works backward from:
A) The nature of justification by faith as taught by and provided by Jesus Christ
B) The way in which the original promise to Abraham was intended to benefit all nations
C) The consistent failure of the Jews to uphold the law that they had been given as a covenant, and the implications of the curse that comes with the failure to do so
The common sense understanding of the word "seed" in Genesis 13:15-16 is that it is being used like the word "fish" or "deer", since it is being used its immediate context to be as innumerable as the "dust" and the "stars". I don't know whether anyone would have ever referred to someone as having "seeds" to refer to their having multiple offspring as opposed to having just one offspring, and I don't know if "seed" as synonymous with "offspring" was ever understood to be anything other than a non-count noun.
Nevertheless, in Galatians 3:16 Paul interprets that the singularity of the word "seed", as opposed to "seeds", is due to something that was encoded into God's covenant with Abraham (and possibly, by extension, even encoded into the Hebrew language) that was not to be understood until the time of Christ. To Paul, the use of “seed” in Genesis as a singular word, as opposed to “seeds”, is indicative of the singularity of Christ as a single man.
Having established the importance of the singularity of "seed", Paul deals with the non-count aspect of "seed" as something that refers to all those who are counted as being part of Christ.
It is on the basis of both the singularity aspect and the non-count aspect of "seed" that Paul understands God's covenant with Abraham's "seed" as one in which Christ Jesus is the primary Recipient of the covenant, while Abraham and everyone who operates by faith are the secondary recipients (Galatians 3:29). It is with this understanding, parsing the word "seed" that Paul is able to refract the covenant of Abraham into an understanding of justification through faith in Christ Jesus. Christ Jesus—as the primary recipient of the covenant— lived the covenant perfectly and could thus extend the blessings of the perfectly-followed covenant to all those who had failed. Paul is then also able to deal with how the covenant extends blessings to all nations, as the covenant extends, secondarily, to all those who are connected to Jesus.
Paul advances this idea of how people are connected to Christ/the Seed by interpreting Abraham's biological descendents to be symbolic of those who would have faith as Abraham had faith, and thereby be “children of Abraham” (Galatians 3:7). Paul further advances this idea with his analysis of Hagar vs. Sarah in Galatians 4:21-28. To Paul, it is Ishmael, who was born of biological means that were not specially assisted by the Holy Spirit in the womb of Hagar, who is representative of those born to Abraham only biologically. To Paul, it is Isaac, who was born by means that were specially assisted by the Holy Spirit in the womb of Sarah and born of a specific promise, who represents all who are born of the Spirit.
In same manner that the blessing extends secondarily to people beyond Jesus, so too does the curse of not following the covenant extend secondarily to people beyond Jesus. It is this curse that Jesus—being the primary Recipient of the covenant—bore for all those people who are secondary recipients of it. It is this that enables people who have faith in Jesus to be free of the curse that they, secondarily, bear.
In regard to the promise that is given to the "seed" in Genesis 17:7-9, to Paul, the “land” of Canaan that is presented to Abraham in literal terms, is for Paul symbolic of the promise of all of God’s blessings that would come through the Seed/Christ and to all who are part of the Seed/Christ. In his analysis of the meaning of Hagar and Sarah in Galatians 4:21-28, Paul talks of the “Jerusalem above” that is the actual blessing of the promise to Abraham as opposed to the “Jerusalem below”.
Based on how Paul organizes the covenant into its primary and secondary recipients, Paul makes a distinction between the aspect of the covenant that extends from God to Abraham and the aspect of the covenant that extends from Abraham back to God. While the latter aspect of the covenant is indicative of the binding covenant that was dealt with by the covenant’s primary Recipient, the former aspect of the covenant is indicative of God’s unending and unbreakable promise to the Recipient and to all the secondary recipients whose covenant failures are covered by the Recipient.
For the secondary recipients, the aspect of the covenant that extends from God to Abraham is an unending promise to Abraham and his heirs that would not be breakable despite any future failures that Abraham's heirs might have. As such, it was a promise that was not bound by whether those secondary recipients unfailingly followed the covenant. As such, the promise could not be supplanted by any future covenant that was based on whether secondary recipients were successful in following that covenant (Galatians 3:17).
It is on this basis that Paul makes a substantive distinction between what is at the core of the covenant of Abraham and the covenant on Mount Sinai. As Paul says in Galatians 3:19-20, it is Christ, who is one with God, whom Paul considers to be the Seed, whom Paul distinguishes from those who received the law on Mount Sinai through a “mediator”, since a mediator mediates between two different parties. Paul does not consider the promise to the Seed as something that could be broken by the Jews' failure to obey the covenant on Mount Sinai because the covenant on Mount Sinai was made directly to the secondary recipients of the covenant of Abraham.
To Paul, the circumcision that was woven into the covenant of Abraham was symbolic of commandments that were to be given 430 years later on Mount Sinai and that would carry the explicit threat that secondary recipients would be abandoned by God if they failed to obey the commandments. Circumcision, in the context of the law, says, “may I be cut off from my descendents if I don’t keep the law”. In this way, the circumcision was a “proto-law” given symbolically 430 years before Mount Sinai that would contain binding language bearing blessings to those who followed it and threats to those who didn't.
Paul says that circumcision was symbolic of the full weight of the law covenant and its threats that the Israelites needed to be 1) presented with and then 2) need to be freed from in regard to their obligations to it as a covenant. The law, though it could never be the basis for a lasting and binding covenant, was presented to the Israelites on Mount Sinai as though it were a binding covenant for a period of time in order to tutor the Israelites to give them enough of an understanding of the law until the “faith should be revealed” (Galatians 3:23-25). When the "faith was revealed", the law would not be destroyed, but its purpose would be re-oriented. The binding language of the law would be directed away from secondary recipients and onto its primary Recipient (who had been the true Recipient all along). At that point, the law would no longer be presented as a binding contract to secondary recipients but would be subservient to the requirements of faith in the lives of secondary recipients.
To Paul, it is in Christ that the true purpose of circumcision was revealed: that circumcision was an indication of the curse that people where bound to when they failed to perfectly follow the covenant of Abraham and the law perfectly. It is circumcision that was intended to operate in primarily as symbolizing the covenant between God and the Recipient. It was this curse that secondary recipients of the covenant were freed from when they accepted the perfection of the primary Recipient as a covering. It is for this reason that Paul, knowing the full revealed meaning of circumcision in the context of Christ, says to the Galatians in 5:2-3, "if you allow yourselves to be circumcised, Christ will be of no value to you at all".