In Genesis 12:3 God says to Abraham, in you, all nations shall be blessed. That one word “blessed” actually means grafted in Hebrew. So what Genesis 12:3 is actually saying is that in Abraham all nations shall be grafted. Genesis 26:5 says Abraham obeyed my Torah (my instructions or what we know today as the law of Moses). So because Abraham believed Yehovah and obeyed His Torah, He was righteous by faith. And because he walked out obedience to the Torah, the nations would see him being obedient and desire to be grafted.
If you compare this with Romans 2:29 where it says the true Jew is the one who is obedient to the Torah. And Deut 31:10-12 with Isaiah 56:3 where it says the stranger in Israel is expected to obey the Torah. Compare this Click here to read more