The "land" referred to here is Persia (roughly Iran today, not Israel). Many non-Jews lived in Persia and surrounding regions, but our text says that "many" of these "became Jews." In other words, non-Jews (Gentiles) became Jews. Becoming a Jew depends more on trusting in the true and living God than on who gave birth to you.
Some today would affirm that one cannot be both a good Jew and a good Christian, but this is disproved by the fact that the earliest followers of Jesus were mostly Jews. In fact, Jesus Himself was born of a Jewess and was the adoptive son of a Jew. Being Jewish and Christian at the same time, therefore, is compatible.
Consider the words of the Jew, Paul. His Jewish credentials were about as good as any, but he had no difficulty affirming allegiance both to the God of Abraham and to the Lord Jesus Christ. He wrote that a Gentile who receives Jesus into his heart actually becomes a child of Abraham and participates in God's promise to Abraham.
Galatians 3:24-29: "Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith. But after that faith is come, we are no longer under a schoolmaster. For ye are all the children of God by faith in Christ Jesus. For as many of you as have been baptized into Christ have put on Christ. There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus. And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise."
Jesus was and is the greatest Jew ever born into the world. May all who trace their physical roots to Abraham rejoice with him in Jesus. PGH