Paul's analysis of Abraham's "offspring(s)" in Galatians 3 In Paul's letter to the Galatians, he talks about (among other things) how God's promise to Abraham was fulfilled in Christ. Galatians 3:16 reads (in the NRSV; other translations may say &quot;seed&quot;, &quot;progeny&quot;, &quot;descendants&quot;, etc.):

Now the promises were made to Abraham and to his offspring; it does not say, &quot;And to offsprings&quot;, as of many; but it says, &quot;And to your offspring&quot;, that is, to one person, who is Christ.

Elsewhere he says that &quot;those who believe are the descendants of Abraham&quot; (3:7) and &quot;if you belong to Christ, then you are Abraham’s offspring, heirs according to the promise&quot; (3:29).
In Genesis, there are several promises (or repetitions of a promise) made to Abraham, including:

Then the Lord appeared to Abram, and said, &quot;To your offspring I will give this land.&quot; (12:7)
On that day the Lord made a covenant with Abram, saying, &quot;To your descendants I give this land&quot; (15:18)
&quot;I will establish my covenant between me and you, and your offspring after you throughout their generations, for an everlasting covenant, to be God to you and to your offspring after you. And I will give to you, and to your offspring after you, the land where you are now an alien, all the land of Canaan, for a perpetual holding; and I will be their God.&quot; God said to Abraham, &quot;As for you, you shall keep my covenant, you and your offspring after you throughout their generations.&quot; (17:7-9)
&quot;I will indeed bless you, and I will make your offspring as numerous as the stars of heaven and as the sand that is on the seashore.&quot; (22:17)

It seems that in Genesis, the promises are actually speaking about many descendants and not just one person, regardless of the grammatical detail. Certainly the appearances in chapters 17 and 22 are talking about many people in many generations.
So isn't Paul just making a totally unsupported argument? And why does he make it at all, given that a few verses before and after, he is happy to consider plural offspring (all believers)?
Evangelicals defend this analogy by arguing (1) that even in the original context, "Abraham's offspring" did not refer to all Abraham's physical descendants, (2) that "Christ" can be interpreted as a spiritual descendant, not merely a single physical descendant, and (3) that the context, particularly Galatians 3:28–29, demonstrates that Christians are joined together in Christ as descendants of Abraham.

First of all, we know that "Abraham's offspring" cannot refer to all the descendants of Abraham: John Calvin points out that in Genesis 21:12, the offspring is limited to Isaac, and then later again Esau is excluded.  Thus, Paul is arguing here that "offspring" cannot refer to all Abraham's biological descendants, but only those who are called by God.  Calvin writes (using seed as a synonym for offspring):


  He merely shows that the word seed must denote one who was not only descended from Abraham according to the flesh, but had been likewise appointed for this purpose by the calling of God.


So how do we get from "those who are called" to a single "offspring"?  Like Calvin, Jamieson, Fausset, and Brown argue that the single "offspring" is the unified body of Christ, with Christ himself at the head:


  one … Christ—not in the exclusive sense, the man Christ Jesus, but "Christ" (Jesus is not added, which would limit the meaning), including His people who are part of Himself, the Second Adam, and Head of redeemed humanity. Ga 3:28, 29 prove this, "Ye are all ONE in Christ Jesus" (Jesus is added here as the person is indicated). "And if ye be Christ's, ye are Abraham's SEED, heirs according to the promise."


That is, the singular "offspring" refers to Christ, considered generally: the redeemer, as opposed to the biological descendant of Abraham.  Abraham's offspring, thus, is Christ, and all those who are joined to him through redemption, both from Abraham's biological descendants, and from his non-biological descendants.  As JFB states, Galatians 3:28–29, just a few verses later, makes this plain:


  28 There is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus. 29 And if you are Christ's, then you are Abraham's offspring, heirs according to promise.


The Greek word translated "offspring" in v. 29 is the same word that is used earlier.  Thus, by virtue of being "one in Christ Jesus," all Christians are Abraham's "offspring," in the singular sense of offspring.

The New Bible Commentary (1970) summarizes:


  The divine agreement referred, says Paul, not to the plurality of Abraham's natural descendants, but to his offspring, seen to be Christ as the head of a new race.  The sense is not to successive generations of men, but fulfillment in one kind of offspring, which is summed up in Christ.  This interpretation is not evident in the language of Gn. 12:7; 13:15; 17:7, 8, and 22:18, but neither is it excluded.