Living a Christian life is a radical choice. It is about having one all-consuming purpose, which is to be a disciple of Jesus Christ. 
Jesus Himself told us, ‘If anyone wants to come after Me, let him deny himself and pick up his cross daily and follow Me’ (Luke 9:23). He also said, ‘None of you who doesn’t give up all his possessions can be My disciple’ (Luke 14:33). And He even went so far as to say, ‘If someone comes to Me and doesn’t hate his own father and mother and wife and children and brothers and sisters, and even his own life, he cannot be my disciple’ (Luke 14:26). None of these sayings is meant to be taken strictly literally. But they show clearly that Christian discipleship is a radical, all-encompassing thing.  

Similarly, the apostle Paul set us a precedent when he stated, ‘For me, to live is Christ’ (Phil 1:21). He also said that he considered everything ‘filth’ so that he might gain Christ (Phil 3:8). Like the Lord Jesus, then, Paul saw the Christian life as one that is about giving our all for Christ, about making our lives count to the maximum in His service until the day we die or He returns. Nor do any of the other New Testament writers lead us to believe that the Christian life is anything less radical than this.

When it comes to the decision of a Christian to marry someone, then, this decision needs to be made as part of the goal of living only for Jesus. If marrying a certain person is going to better enable a believer to do this, then it is to be welcomed, but if it is going to hinder that believer doing this, then it needs to be avoided.

It should therefore be obvious that the idea of a Christian marrying a non-Christian is deeply problematic. If someone’s goal in life is to live only for Christ, how can there not be massive problems involved if that person joins their life at the most intimate level with someone who does not have the same goal?

It comes as no surprise, then, that the Bible strongly implies that Christians should not marry non-believers. Paul’s words in 2 Corinthians 6:14-18 are relevant in this respect, and are worth quoting in full:

14 “Do not be unequally yoked together with unbelievers. For what partnership do uprightness and lawlessness have, or what fellowship does light have with darkness? 15 And what harmony does Christ have with Beliar? Or what does a believer have in common with an unbeliever? 16 And what agreement does the temple of God have with idols? For we are the temple of the living God, as God said: ‘I will live in their midst and walk among them, and I will be their God and they will be my people. 17 Therefore, come out from among them and be separate, says the Lord, and do not touch what is unclean. Then I will welcome you 18 and I will be a Father to you and you will be sons and daughters to me, says the Lord Almighty.”

What is said here about not being unequally yoked with unbelievers surely applies in part to marriages between Christians and non-Christians. It would be a very strained interpretation that excludes marriages from what Paul is saying. We should not hesitate to say, then, that in this passage Paul is strongly implying that Christians should avoid marrying non-Christians. And, given the radical nature of Christian discipleship, this is exactly what we would expect the Bible to teach. (Verse 17 should not be understood to mean that Christians who are already married to non-believers must leave their spouses. See 1 Cor 7:12-13.) 

The value of this teaching can be seen time and time again in churches. Those believers who are married to non-Christians often have a terribly difficult time trying to live out their lives in following Jesus. Either they do try to live for Christ alone, and great hostility from their spouse results. Or, frequently, they end up compromising on their discipleship.

In fact, Christians should not only avoid marrying non-believers, but they should also avoid marrying believers who are not serious about giving their all for Jesus. Being married to a half-hearted Christian is almost certain to hinder someone’s discipleship.

Although, as a general rule, it is a grave mistake for a Christian to marry a non-believer, I do think that there are very rare circumstances in which it is God’s will.

I am thinking especially of situations in which the alternative involves a real danger of being murdered. There are well-attested accounts of this from the Muslim world. What sometimes happens is that a teenage girl from a Muslim family becomes a Christian. Her father nevertheless arranges for her to marry a young Muslim man, but she refuses, whereupon the father threatens to kill her unless she agrees. When the girl continues to refuse, sometimes the father then makes good on his threat to kill her.

No one should doubt that murders for this and similar reasons sometimes take place. These are so-called ‘honour killings’, which are well-documented both in some Muslim countries and in the Western world. 

I think that in at least most situations of this kind it would be the will of God for the girls to agree to marry non-Christians if they believe there is a genuine threat to their lives. Although their ability to achieve things for Christ will be greatly hindered by their marriage, it seems to me unlikely that refusing to marry a non-believer is typically something that is worth being martyred for. I wouldn’t rule out that God may at times want a girl in this sort of situation to become a martyr, but I think these girls should marry the non-Christians unless they believe God is specifically telling them to do otherwise. (It is morally acceptable for Christians at times to do unpleasant things in order to save their lives, but they must never deny that they are believers. On this, see, e.g., Matt 10:32-33.)

Other than for the purpose of avoiding being murdered, I do think that there may be other, extremely rare situations in which it might be God’s will for a Christian to marry a non-Christian. But there would need to be a very good reason indeed for doing something that on the face of it would be so harmful to Christian discipleship.

In the vast majority of situations, marrying a non-Christian would be a terrible mistake for a Christian to make. Our goal in life is to give our all for Jesus, and only things that help towards this goal are acceptable. a Christian life is a radical choice. It is about having one all-consuming purpose, which is to be a disciple of Jesus Christ.  Jesus Himself told us, 'If anyone wants to come after Me, let him deny himself and pick up his cross daily and follow Me' (Luke 9:23)....