Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness? – 2 Corinthians 6:14.
Few other Scriptures have produced more difficulty for God’s servants — ministers, pastors, elders — as they have sought to serve others. While not applying only to marriage, it almost certainly applies as a warning to a believer thinking about marrying an unbeliever. It is a Spirit-inspired reminder that when we make life-long partnerships with those who do not share our deepest values in Christ, we are endangering our spiritual health and placing future misunderstandings and burdens on our partnership. Just as God’s Law would not allow the Israelites to yoke a donkey and an ox together because it would ultimately break them both down, Paul also reminds Christians this same principle is true for their most significant relationships as well.