The Jewish people are prohibited biblically of marrying out of the faith. The main worry concerns Jewish men who take wives outside the faith because tradition is perpetuated through the maternal line. His children are considered lost.
From a Catholic perspective, disparity of worship renders void the marriage of a Christian with an infidel, that is, of a baptized person with one who is unbaptized.
They, therefore, who rashly and heedlessly contract mixed marriages, from which the maternal love and providence of the Church dissuades her children for very sound reasons, fail conspicuously in this respect, sometimes with danger to their eternal salvation. This attitude of the Church to mixed marriages appears in many of her documents, all of which are summed up in the Code of Canon Law: "Everywhere and with the greatest strictness the Church forbids marriages between baptized persons, one of whom is a Catholic and the other a member of a schismatical or heretical sect; and if there is, add to this, the danger of the falling away of the Catholic party and the perversion of the children, such a marriage is forbidden also by the divine law." (Papal Encyclical, Casti Connubii, 31 December 1930).