Pastor John Piper was asked “What can I say to my Christian friend who just got engaged to a non-Christian?” and this was his answer:
The key text is in 1 Corinthians 7:39 where it says that a woman is “free to be married to whom she wishes, only in the Lord.”
That little phrase “only in the Lord” is added to an otherwise innocent marriage to say, “Don’t go outside of the Lord to marry.” So make sure that she knows that that is there, so that she is dealing with truth. […]
In general I would take her (or him, because this can apply to guys too) to the text to show her what it says, and then I would encourage her that the right understanding of it is that Christians should only marry Christians. […]
How can you be intimately, psychologically, spiritually, physically involved with a man who does not say “Jesus is Lord,” a man who doesn’t love your Savior? […]What is at root here is that she is loving this man more than she is loving Jesus. Because if she really loved Jesus—and he was satisfying to her, and her best friend, and walked with her, and talked with her, and sustained her—then the fact that he doesn’t love Christ but says, “I don’t want anything to do with him. He’s not my Lord. He’s not my Savior. I think that’s mythological and foolish,” that should tear her apart emotionally.
What is she saying by delighting in him when the essence of him is anti-Jesus? That’s who he is, he’s anti-Jesus!
I used to believe this, but it sounds strange and cult-like now. Christians can only marry Christians? That sounds as absurd as saying “Atheists can only marry atheists!” or “Hispanics can only marry Hispanics!”
I think it’s crazy and stupid to tell people they can can only marry people inside their religion, race, or nationality.
How ’bout you?