I think Paul is just saying that this is a promise and so has nothing to do with law or conditions.
I agree Paul is saying that the promise predates the Law.
I was asking about the Law that could not impart righteousness, the one that held those under it captive as they were made curses for their disobedience (and that Jesus was made a curse under it for hanging on a tree).
Paul later speaks of that Law as a covenant which had conditions.
That is the Law I was asking about (the Law of Moses).
The problem with viewing no difference between Jew and Gentile as far as this Law goes is Paul directly states that there was a difference.
The covenant God made with Abraham was to his Seed, and this older covenant (430 years before the Law, the "Old Covenant") was not invalid because of the Law.
The purpose of the Law was added because of transgressions until the Seed would come to whom the promise had been made.
You are right that there is neither Jew nor Gentile in terms of being one in Christ.
But this was not true of the Law. The Law was very specific about applying only to Israel as a nation. Israel was a nation created by God to be a unique people set aside from the Gentiles. The Law was a covenant with this nation.
I think what you may me missing is the purpose Israel was created. It was through this people who were held captive by the covenant God had made with them (the Old Covenant) by their own disobedience. This was a temporary covenant as it was designed to keep this people until the "Seed would come to whom the promise had been made".
At no time in the Bible is the Law (the Old Covenant) said to apply outside of Israel.
This is important, otherwise the words that salvation came "first to the Jews and then to the Greeks" only means the gospel was first preached to the Jews (almost happenstance). The significance of salvation first coming to the Jews, of the Samaritan woman's conversation with Jesus, and of redemptive history is lost.
Also, Paul emphasizes the importance of the Jews being under the Law. If we think this applied to everybody what on earth do we do with that passage? Chalk it up to mystery even though it was important to Paul's explanation?
For salvation to come to all the Law had to be fulfilled and canceled. Jesus was made a curse, in this way, for every person. But He did not deliver Gentiles from the curse of the Law as Gentiles were not under the Law.
He redeemed all from the bondage of sin and death. All were under this bondage. But the Law was a covenant with Israel, and it showed them their sins, keeping them captive until the Promise came.