Saul writes to Jews and Jewish Christians. This is evident in these passages:
23 But before faith came, we [JEWS] were kept under the law, shut up unto the faith which should afterwards be revealed.
24 Wherefore the law was our [JEWS] schoolmaster to bring us [JEWS] unto Christ, that we [JEWS] might be justified by faith.
25 But after that faith is come, we [JEWS] are no longer under a schoolmaster.
26 For ye [JEWS] are all the children of God by faith in Christ Jesus.
27 For as many of you [JEWS] as have been baptized into Christ have put on Christ.
28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye [JEWS] are all one in Christ Jesus.
29 And if ye [JEWS] be Christ’s, then are ye [still JEWS and] Abraham’s seed, and heirs according to the promise. Galatians 3:23–29.
Gentiles were NEVER under the Law. Gentiles were NEVER under a "schoolmaster" (the Law.)
And the word "Greek" in verse 28 is "Hellens" which refers to Greek-speaking and raised Jews of the Diaspora. It is NOT the word for Gentiles. Take a look at the words in bold/underline/italics. Saul is definitely writing to Jews and Jews were under the Law since at least Moses in the desert at the time of the Tabernacle.
The context of these words written to Jews by Saul was to alleviate their concern of being followers of a man named Jesus and what that meant to them as followers of Moses and Abraham. Saul tells them that if they (belonged) to [Jesus] Christ they were STILL Abraham's seed and heirs according to the Promise.
The Abrahamic inheritance follows a biological line from Abraham, to Isaac, to Jacob, and to Jacob's twelve sons (or tribes.) The twelve tribes are Israel and they are the biological seed of Abraham and heirs of the Promise. Gentiles do not come from Abraham's loins. They come from Ham and Japheth. They were NEVER biological heirs to Abraham. NEVER.
Your interpretation falls short of the Word of God.
Saul is writing to Jews.
JEWS.
"O foolish Galatians, who hath bewitched you, that ye should not obey the truth, before whose eyes Jesus Christ hath been evidently set forth, crucified among you? 2 This only would I learn of you, Received ye the Spirit by the works of the law, or by the hearing of faith? 3 Are ye so foolish?
having begun in the Spirit, are
ye now made perfect by the flesh? 4 Have ye suffered so many things in vain? if it be yet in vain. 5
He therefore that ministereth to you the Spirit, and worketh miracles among you,
doeth he it by the works of the law, or
by the hearing of faith? 6 Even as Abraham believed God, and it was accounted to him for righteousness. 7 Know ye therefore that
they which are of faith,
the same are the children of Abraham. 8 And the scripture, foreseeing that
God would justify the heathen through faith,
preached before the gospel unto Abraham, saying,
In thee shall all nations be blessed. 9 So then
they which be of faith are blessed with faithful Abraham. 10 For as many as are of the works of the law are under the curse: for it is written, Cursed is every one that continueth not in all things which are written in the book of the law to do them. 11 But that
no man is justified by the law in the sight of God, it is evident: for,
The just shall live by faith. 12 And
the law is not of faith: but, The man that doeth them shall live in them. 13 Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree: 14
that the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith."
Two things to note. When Paul speaks of Spirit in verse 3, he speaks of faith. When he speaks of the Flesh, he speaks of the Law. So again, what you say about the Law and covenants means nothing. Paul comes right out and condemns the Gentiles here for coming to Christ in faith, but listening to the Judaizers believing they are perfected by the Flesh/Law. Also for hellens, consider it like Romans. He speaks to the cultured, next to the uncultured. It includes non-Jewish Gentiles who are a law unto themselves, who have come to Christ by faith. Paul isn't saying, there is neither Jew nor Jew, is he? Again, do note that Paul had Timothy get circumcised. Why? He was part Jew. However, Paul did not have Titus get circumcised. Why not? Titus was not Jewish, just Gentile. Would you say that Titus was not saved? Did Paul really consider a non-Jewish Gentile to be his friend, and coworker in Christ. (Quick answer... YES. I mean, Paul even wrote a book to him.)
In the verses above there is that word ethnos [Gentiles] which never means mixed race Jews, because mixed race Jews are not a race. It speaks of non-Jewish Gentiles. One can also know because it says that the blessing of Abraham (in thee all nations shall be blessed) might come on the Gentiles THROUGH JESUS CHRIST. Something important to note is that the blessings of Abraham belongs to the Jews who have faith, because they are descendants of Abraham. For the Gentile, it says the blessings come upon them through Jesus Christ, not by being descendants of Abraham. The only thing that Gentiles have in common with Abraham is faith, and it is by that faith that the blessings come upon them through Jesus Christ. I still don't get how you are so blind to this. The Abrahamic covenant is separate from the promises from which the Gentiles have blessings come upon them through Jesus Christ. How? The Abrahamic covenant has a sing, circumcision. The promise only has faith as the base. Paul had Timothy, a mixed race Jew get circumcised. Why? A mixed race Jew that had chosen his Jewish heritage. Paul had Titus NOT get circumcised. Why not? Titus was Gentile and thus not a part of the Abrahamic covenant. This speaks to the unconditional nature of the Abrahamic covenant.
Also, your ignorance truly shows through your statement that Gentiles are not biological heirs to Abraham. That is you believing that salvation is through the flesh. Biological = flesh. The Law = the flesh. Faith = the Spirit. Non-Jewish Gentiles who believe in Jesus Christ by faith are SPIRITUAL descendants of Abrahams, and have thus had the blessings of the promises God made to Abraham come upon them through Jesus Christ. Not by being biological heirs to Abraham, which would make them a part of the Abrahamic covenant, but by being spiritual heirs of Abraham by faith, which puts them under the promises God made to Abraham. NOT THE COVENANT. The promise that says that all nations would be blessed through the seed of Abraham (Jesus Christ.) Again, I don't know why you seem incapable of seeing that which is hidden from natural man, as it is spiritually discerned.