For what partnership is there between righteousness and lawlessness? 16 What agreement has the temple of God with idols?Or what fellowship is there between light and darkness? For we are the temple of the living God; as God said, "I will live in them and walk among them, and I will be their God, and they shall be my people.One of the major problems Paul faced in Corinth was the difficulty new converts there had in living out Christianity ethically in everyday actions.
The book of Ruth tells a delightful story of a foreigner who became part of the lineage of Christ.
Religiously, it was extended to things like using two different kinds of animals yoked together for plowing.
It was not just a legalism, but an attempt to live out in all aspects of life what they understood to be God's purposes for his world that he had created.
The harlot, Rahab, also of another nation, is included in the lineage of Christ as recorded in Matthew 1.
Colossians makes it clear that from God's perspective all are one in Christ.