Statistics show that a married couple who believe in the same faith are more likely to stay married longer. Paul speaks on this in 2 Corinthians 6:14:

Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness?

He uses a metaphor that farmers would understand. Two oxen “yoked” together must agree to travel in the same direction or they will be fighting and striving against one another. An unequalled yoke causes divisiveness and struggle.

If they are already married, they should not divorce over spiritual matters. Paul explains this thought also:

To the rest I say this (I, not the Lord): If any brother has a wife who is not a believer and she is willing to live with him, he must not divorce her. And if a woman has a husband who is not a believer and he is willing to live with her, she must not divorce him. For the unbelieving husband has been sanctified through his wife, and the unbelieving wife has been sanctified through her believing husband. Otherwise your children would be unclean, but as it is, they are holy. 1 Corinthians 7:12-14

This is “Paul’s” wisdom, he makes clear. It is not a scriptural promise of salvation for the unbelieving partner--just good advice to a married couple. If an “unequally yoked” couple are married, the hope is that the wife’s genuine faith would entice the husband and children to become a Christian (sanctify or “clean up” their act), but sadly the one spouse may live with the notion his/her whole life that they will not see their married partner in heaven. This is not an ideal situation, but it has worked.