Question:

What does the Bible say about marrying a non-Christian?

Answer:

Problems arise when a Christian marries an unbeliever.  Marriage makes two people become one on the level of body.   
 
Christians have been changed in their spirits and in their souls.  The soul is another word for heart or mind.  All people have three parts, spirit, mind, and body.  The spirit of the Christian has been joined to the Holy Spirit.  Now, if the Christian joins his or her body to the body of someone who has a different spirit than the Holy Spirit, that is a conflict automatically.  Before a Christian comes to believe, he or she is in bondage to Satan.  The unbelievers are dead to God in spirit, mind, and body.  When they receive Jesus, they become alive in their spirit and somewhat in their minds.  From that day on, they are fighting with Satan for the mind.  They are directing their mind to the Holy Spirit by acknowledging God.  They turn their attention to God.  God is Love, so they are turning their attention toward the only real Love that there is.  
 
This is why the Bible says, "Do not be yoked together with unbelievers." 2 Corinthians 6:14  A yoke is a big wooden thing that is put across two oxes so that they can pull a plow together.  When two people get married, they have a shared burden and they have to pull together.  When they disagree at the core of their being, in their spirits, they cannot pull together.  One or the other has to concede.  
 
The Bible goes on to say that one is in righteousness (the righteousness of Jesus) and the other is in wickedness (because they have not come to Jesus).  It says that one is in the light and the other is in darkness.  What does righteousness and wickedness have in common what unity can light have with darkness?  The answer is, None. There can be no unity.  They can fake it, but that's about it.  
 
This lack of unity is so bad that the Bible says that if the unbeliever wants to leave the marriage, let them go.  1 Corinthians 7:15  
 
The Bible goes on to say, What agreement does Christ have with the evil one?   Unbelievers are slaves to the evil one.  They can't help it unless they come to Christ.   
 
Then the Bible asks "What do the believer and the unbeliever have in common?  What agreement does the temple of God (which you are) have with idols.  Can the temple of God bring in false gods?"  
 
Then, it says that Christians are the temple of the Living God and He will dwell in them and walk in them and He will be their God and they shall be His people.  
 
For this reason, it says, that Christians must come out from among unbeliever and be separate.  God says, "Don't touch the unclean thing."  
 
God is very strong on this point because He wants you to be happy.  He doesn't want to see you always sad for years or to have a marriage that breaks up with pain for you and the children.  
 
Now, none of this means that you cannot witness to unbelievers, but you can never have unity with them until they come to Christ in a real way.  You can love them.  God tells us to love every person.  You are showing your love for them as you witness to them.