Believers were taking unbelievers as a spouse. We must listen to what the Bible says and what it does not say. The New Testament strongly emphasizes the unity of the human race. In Christ all previous religious, cultural, and social barriers are destroyed. The primary marriage restriction given in the New Testament parallels that of the Old Testament.
Nothing is said of cultural or racial sanctions.
But this was for cultural reasons, not Biblical reasons. Though this attitude is wrong, the effects of it must still be recognized. Based on where people live, they or their children may face prejudice from others. While that is wrong, it must be considered. If a man and woman are totally committed to living for Christ, then they will have the capability through the power of the Holy Spirit to resolve any difficulties that might arise from those other areas.