The Bible exhorts a believer not to marry outside the faith. This doesn't have anything to do with denominations--our Baptist daughter married a Presbyterian and is active with her husband in their church. But the prohibition does mean children of God are to marry other children of God.
Moses cautioned the Hebrews when they approached the Jordan that they weren't to enter the Promised Land and take Canaanite wives (Deuteronomy 7). The Canaanites were morally corrupt and worshipped false gods. In the view of ancient Israel, they were like a contagion that might infect God's people and make them spiritually sick; thus Israel needed to stay away from them. Two Hebrew leaders--Ahab and Samson--did marry Canaanites, and they failed miserably in their spiritual mission. The names of their wives are synonymous with evil: Jezebel and Delilah.
My eighth-grade teacher used to say, "The best thing in the world is a good girl, and the worst thing in the world is a bad girl." I always thought this was unique to her until I read Proverbs 5 and Proverbs 31. The latter chapter tells us about the godly woman whose husband and children rise up to bless her as a woman of virtue. However, the woman in Proverbs 5 is a cunning woman lying in wait for some unsuspecting man to ensnare and ruin. And it's true that these words aren't really gender-specific since men can be the culprit, too.
The New Testament is equally clear. The Apostle Paul wrote, "Do not be unequally yoked with unbelievers" (2 Corinthians 6:14).
I've had many young people tell me their unbelieving fiancés promised to join them in church after they married, and have seen many of these promises die a slow death.
She was raised in a Baptist church and also attended a local Pentecostal church as a child. She began performing at age 11 in the junior gospel choir at New Hope Baptist Church in Newark, NJ. Her first solo performance was "Guide Me, O Thou Great Jehovah." As a teenager she attended Mt. Saint Dominic Academy, a Catholic school in Caldwell, NJ.
Whitney Houston had the voice of a generation. She sold millions of records and had a flourishing film career.
But Houston married a Canaanite. This woman, influenced by three Christian churches as a child, saw her life take a downturn. She died at age 48 after drowning in her bathtub. Toxicology found marijuana, Xanax, Flexeril, Benadryl and cocaine in her system. But the tragedy continued when her 22 year-old-daughter died earlier this year in a remarkably similar way: drowning with drugs in her system.
Not every case is this dramatic, but God's warning must be heeded.