Since we’re all really just one race, why did God tell Jews not to marry Gentiles? Does this mean there are actually two races: Jew and Gentile?
The Bible does indeed teach that we are all one race in the sense that we all came from one man (Acts 17:26). However, the Bible also acknowledges different races in the sense of different peoples or ethnicities. John spoke of witnessing “a great multitude that no one could number, from every nation, from all tribes and peoples and languages” (Rev. 7:9). “Peoples” comes from the Greek term laos, referring to one’s own populace or nation or tribe or people group, “all those who are of the same stock and language.” “Tribes” comes from the Greek term phyle, defined depending on the context as a “race or clan,” “kindred, tribe.” “Nations” comes from the Greek term ethnos, the term from which we get our word ethnicity. It is defined by Strong as “a race” or “a tribe,” and is also the same word used in both the Old and the New Testament to refer to Gentiles or non-Jews. Luke writes of Jews living in a variety of Gentile nations (Acts 2:7-11), showing that while all Gentiles by definition are not Jews, Gentiles themselves are divided up into a multitude of different nations, tribes, and ethnicities.
Thus, we conclude that the Bible teaches that we are all one race, i.e., the human race, in that we have all descended from Adam and are all created by God with the same basic human spirit and biology. The Bible also points out that since Babel (Gen. 11:1-9), this one human race is divided up into a variety of different groups based on similarities in language, stock, tribe, and kindred. The biblical teaching that we are all one in spite of these racial or ethnic differences (Gal. 3:28) and should love our neighbor as ourselves (Lk. 10:25-37) condemns racist attitudes and actions such as demeaning, thinking less of, or treating badly any of our fellow human beings simply because they are ethnically different in some way than us.
So why did God command the Jews of the Old Testament to not marry Gentiles? God had set Israel apart from the other nations basically because he had determined that the Savior of the world would come from Abraham’s descendants (Gen. 12:1-3; cf. Gal. 3:8, 16). The decree that they should not marry Gentiles was designed to keep them separate from the other nations and thus holy (Deut. 7:1-4, 6). That is also why they were given a special law and a special, ritualistic system of worship which was designed to separate them from the other nations (Ex. 19:5-6; cf. Eph. 2:14; Gal. 3:24-25; Heb. 9:1-10).