Your concept of God makes a big difference. Did God choose the Jews to be an isolated people, to keep to themselves and to not share the blessings with anyone or any other nation? God didn't want them to become like the other nations but He did want others to worship Him and learn about His love through the Jews. If someone wanted to worship God like the Jews, could they become a Jew?
Mat 12:46 While he yet talked to the people, behold, his mother and his brethren stood without, desiring to speak with him.
Mat 12:47 Then one said unto him, Behold, thy mother and thy brethren stand without, desiring to speak with thee.
Mat 12:48 But he answered and said unto him that told him, Who is my mother? and who are my brethren?
Mat 12:49 And he stretched forth his hand toward his disciples, and said, Behold my mother and my brethren!
Mat 12:50 For whosoever shall do the will of my Father which is in heaven, the same is my brother, and sister, and mother.
If i do the will of the Father, God almighty, i become the brother of Jesus and that makes me Jewish.
Rom 2:28 For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh:
Rom 2:29 But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.
For he is not a Jew, which is one outwardly; = Blood means nothing.
Rom 11:15 For if the casting away of them (Jews) be the reconciling of the world, what shall the receiving of them be, but life from the dead?
Rom 11:16 For if the firstfruit be holy, the lump is also holy: and if the root be holy, so are the branches.
Rom 11:17 And if some of the branches be broken off, and thou, being a wild olive tree, wert graffed in among them, and with them partakest of the root and fatness of the olive tree;
Rom 11:18 Boast not against the branches. But if thou boast, thou bearest not the root, but the root thee.
Rom 11:19 Thou wilt say then, The branches were broken off, that I might be graffed in.
Rom 11:20 Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear:
Rom 11:21 For if God spared not the natural branches, take heed lest he also spare not thee.
Rom 11:22 Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off.
Rom 11:23 And they also, if they abide not still in unbelief, shall be graffed in: for God is able to graff them in again.
Rom 11:24 For if thou wert cut out of the olive tree which is wild by nature, and wert graffed contrary to nature into a good olive tree: how much more shall these, which be the natural branches, be graffed into their own olive tree?
If they do not believe in Jesus they are cast away. "because of unbelief they were broken off, and thou standest by faith. " We are grafted in by faith in Jesus, and that means i do not continue to practice the laws that were given to point to Jesus. A Jew that believes in Jesus does not sacrifice lambs for a sin offering because that makes Jesus's atonement worthless.
My faith in Jesus makes me a spiritual Jew. Rom 2:29 But he is a Jew, which is one inwardly.