Just a short brief here. When Paul is dealing with the "promise" he is dealing with the very last of the 12 parts of the Abrahamic covenant. All the other parts deals with physical promises such as a family, a land, a nation etc.. You can read it for yourself. I posted much of the covenant earlier. But the manner of keeping the promise that in his Seed, his one greater Seed, which is Jesus Christ we all will be blessed when we receive the gift of the Spirit to give us a new spiritual birth. We are not made the physical sons of Abraham and this part of the Abrahamic covenant is all that applies to gentiles. The reason it is said we are a son of Abraham is because Abraham is the father of faith in a miraculous son. There was a monumental transition in history when the obedient and faithful Abraham believed that his son through a too old Sarah would be born This son, like all sons that prefigure Jesus Christ is the second born in keeping with the type of being born of the flesh and of the Spirit. Ishmael, born of the flesh and Isaac, born of God, a miracle. All that are born of the Spirit by faith in Christ are sons of God.
Just so you know that the new birth does not disannul all the promises of God to Israel and those who are saved still maintains their identity, check these two passages out.
Galatians - Written 49 AD
Romans - Written 58 AD
Rom 11:1 I say then, Hath God cast away his people? God forbid. For I also am an Israelite, of the seed of Abraham, [of] the tribe of Benjamin.
2 God hath not cast away his people which he foreknew. Wot ye not what the scripture saith of Elias? how he maketh intercession to God against Israel, saying,
3 Lord, they have killed thy prophets, and digged down thine altars; and I am left alone, and they seek my life.
4 But what saith the answer of God unto him? I have reserved to myself seven thousand men, who have not bowed the knee to [the image of] Baal.
5 Even so then at this present time also there is a remnant (of Israel) according to the election of grace.
The point. Paul still identifies as a Jew and with the remnant 20 years after being saved.
Spoken during the last week of the earthly ministry of Jesus Christ before his crucifixion.
Mt 19:27 Then answered Peter and said unto him, Behold, we have forsaken all, and followed thee; what shall we have therefore?
28 And Jesus said unto them, Verily I say unto you, That ye which have followed me, in the regeneration when the Son of man shall sit in the throne of his glory, ye also shall sit upon twelve thrones, judging the twelve tribes of Israel.
29 And every one that hath forsaken houses, or brethren, or sisters, or father, or mother, or wife, or children, or lands, for my name s sake, shall receive an hundredfold, and shall inherit everlasting life.
30 But many [that are] first shall be last; and the last [shall be] first.
Eph 2:18 For through him we both (Jew & gentiles) have access by one Spirit unto the Father.
19 Now therefore ye (gentiles) are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God;
20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
21 In whom all the building fitly framed together groweth unto an holy temple in the Lord:
22 In whom ye also are builded together for an habitation of God through the Spirit.
The church of Jesus Christ, the temple of the Holy Ghost, sits on a Jewish foundation.
Martin, I am in a constant state of growing in my understanding. I think I am correct about these things but also realized that I could have miner details wrong and as I get more light I will certainly adapt. But I cringe at the thought of leading anyone astray. That is why I have given a lot ao thought to these things before I write them.
May the Lord be pleased with my exaltation of his wonderful person and salvation.