“You never know, husband: the way you handle this might bring your wife not only back to you but to God”. 

1 Cor 7:16 EHP 

The pitfalls in marriage are many and varied. Couples disagree on how many children they will have, how they will allocate their income, how important decisions are made, what kind of holidays they will have. They may also differ on matters of faith, and this can be a source of great friction. 
In Corinth (and most other places where there was a Christian group in Paul’s day) it happened that there were women whose husbands were not Christian believers. There were also men whose wives were non-believers. It constituted a tricky problem both for the people involved, the church as a whole and for Paul. The apostle was having to think his way through this and many other matters that were cropping up for the first time. His first instruction was a “call” from God for such a divided couple to live in peace. But then he makes the wonderful suggestion that by caring, and by being faithful and by observing all the things that make for peace, a believing husband might become instrumental in leading his wife to Christ. And similarly for a believing wife. 
The idea behind this verse “has been well expressed by Michael Green: ‘If one of you has been converted since marriage, then there is reason to suppose that the Lord is at work in your family. And you pray, and you try to live a consistent life, so that if your partner is not won by your word, he/she may be won without a word having been said by the godliness of your life’” (D. Prior, The Message of 1Corinthians, p 128). 

Lord, help all those couples who struggle over matters of faith.