Biblical marriage is a covenant between God and man and wife... and a spiritual union (they become one flesh) in which both husband and wife are believers/Christians. And it is a calling from God; God does not call a believing man to be the husband of an unbelieving woman, nor vice versa. However, such a marriage may take place, and God can certainly and often does work through that marriage, eventually calling the unbelieving spouse unto Himself, making him or her a believer, and that's a wonderful thing. I also should say that there's absolutely no justification or admonition for Christians to divorce their spouse solely on the basis that he or she is not a Christian, and in fact quite the opposite; if the unbelieving spouse wants to remain married, the believing spouse is admonished to do so. God, through Paul, is very clear about all these things especially in Ephesians 5 and 1 Corinthians 7 (verse 12, specifically).
This is a larger statement than just concerning marriage, but includes marriage: In God's economy, it was never about ethnicity; He made us all. It was only ever about who was/were His people, those whom He called, justified, and eventually glorified, and that includes not just Jews but Gentiles also, people of every tongue, tribe, and nation. Believers, regardless of ethnicity, are all one in Christ Jesus, and as such make up God's Israel.
Grace and peace to all.