Rom 4
13 For the promise to Abraham and his offspring that he would be heir of the world did not come through the law but through the righteousness of faith. 14For if it is the adherents of the law who are to be the heirs, faith is null and the promise is void.
15 For the law brings wrath, but where there is no law there is no transgression. 16 That is why it depends on faith, in order that the promise may rest on grace and be guaranteed to all his offspring–not only to the adherent of the law but also to the one who shares the faith of Abraham, who is the father of us all,
Did you catch that? IF adhering to the law was related to becoming an heir in any way it would make the promise null and void. So Paul is teaching here that becoming an heir depends NOT on observance to Torah but on faith. To me this implies that Jews, even though we observe the Torah commands will not become heirs simply because of this observance. As well as Gentiles, who even though they observe the Torah out of love for the God of Israel because of their faith, will not because of their devotion to the written law further assure or establish their position as heirs. Paul seems to openly state that observance is not linked to being an heir.
Romans 3 (CJB)
20 For in his sight no one alive will be considered righteous on the ground of legalistic observance of Torah commands, because what Torah really does is show people how sinful they are.
21 But now, quite apart from Torah, God's way of making people righteous in his sight has been made clear - although the Torah and the Prophets give their witness to it as well -
22 and it is a righteousness that comes from God, through the faithfulness of Yeshua the Messiah, to all who continue trusting. For it makes no difference whether one is a Jew or a Gentile,
23 since all have sinned and come short of earning God's praise.
24 By God's grace, without earning it, all are granted the status of being considered righteous before him, through the act redeeming us from our enslavement to sin that was accomplished by the Messiah Yeshua.