Hi ky. Your premise is not true. One must learn to follow the context of the scriptures. The people in Galatia were also mentioned in 1 and 2 Peter as being "strangers." What is that? It is people who are not at home.
1 Peter 1:1
Peter an apostle of Jesus Christ, to the strangers scattered throughout Pontus, Galatia, Cappadocia, Asia, and Bithynia,
These are provinces in Asia Minor.
The reason Paul said in Rom 9 (from which you quoted) that they were not all Israel that are of Israel is a reference to these people who were born physically of Abraham through Jacob and were under the Abrahamic Covenant promises but who had in 722 BC been cut off from those promises by being extracted from the land by the Assyrians because of their sins. He then said of them "not my people" and counted them as "gentiles," but in the same breath said they would be called the "sons of the living God (see Hosea 1), a standing that can only be made possible by the shed blood of Jesus Christ and their new birth. One can see the power of Christ to reconcile all sinners to God and make them new and restore all things.
Can you see the typology between the first born son and the second born son. This is the point of Romans 9. To show that the first birth of the flesh profits nothing but they must experience the second birth through faith in Christ to be children of God. Romans was written in 58 AD and by this time it is abundantly clear that only a very small remnant of the whole of Israel would be saved by the blood of the God Man, Jesus Christ because they held on to their trust in the deeds of the old man, the law of Moses.
Ro 9:5 Whose are the fathers, and of whom as concerning the flesh Christ came, who is over all, God blessed for ever. Amen.
6 Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel:
7 Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called.
8 That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed.
All through the scriptures is this truth illustrated in type beginning with Cain and Abel. The elder - the flesh, the firstborn, shall serve the younger, the second born - the Spiritual man. This is illustrated everywhere. The prodigal in Lk 15 was the second son. Jesus Christ was the second son of God, (Lk 3:38). There is Judah and Israel. Esau and Jacob, Ishmael and Isaac, Japheth and Shem, the old covenant of law and the new covenant of grace to name a few. This principle is most consistent throughout all the scriptures until every entity left on the earth is born of the Spirit.
Jesus Christ could not save anyone under the OT law which was the operative principle of God's divine dealing with his people Judah when he came as a man into this family. He must be born from above, and he was at his resurrection according to the scriptures. After this he could not only save every member of his family but every member of all families on the earth.
Col 1:18 And he is the head of the body, the church: who is the beginning, the firstborn from the dead; that in all things he might have the preeminence.
19 For it pleased the Father that in him should all fulness dwell;
20 And, having made peace through the blood of his cross, by him to reconcile all things unto himself; by him, I say, whether they be things in earth, or things in heaven.
21 And you, that were sometime alienated and enemies in your mind by wicked works, yet now hath he reconciled
22 In the body of his flesh through death, to present you holy and unblameable and unreproveable in his sight:
Do not think you can be saved apart from the cross of Jesus Christ.
Rom 1:3 Concerning his Son Jesus Christ our Lord, which was made of the seed of David according to the flesh;
4 And declared to be the Son of God with power, according to the spirit of holiness, by the resurrection from the dead:
The spirit of holiness is the Holy Spirit.
Flesh first
Spirit second.
1 Cor 15:45 And so it is written, The first man Adam was made a living soul; the last Adam was made a quickening spirit.
If there would have been a way to be saved during OT times, as the NT defines salvation from sin, then there would have been no need for Christ to have died and to have risen from the dead. See 2 Cor 3.
Jn 3:5 Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God.
Jesus Christ is a man and kingdom is God's.
May the Lord be pleased and honored by my handling of his wonderful word.