(This was written in response to a question about whether a Christian should marry or date a non-Christian)
I briefly referred to the topic of Christians and non-Christians marrying in the following sermon:
The bible verse that I mention is 2 Corinthians 6:14 which reads, “Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness?”
The context (see vv. 15-18) refer to religious syncretism, the mixing of Christian and pagan beliefs, and so, this verse is first and foremost a prohibition against such mixing. This is in-line with the first commandment (You shall have no other gods before me.)
In a secondary sense, this passage is also sometimes used as support for saying that Christians should not marry non-Christians (which is the sense that I refer to it in the sermon) or that a Christian should not have a non-Christian as a business partner. This is good advice and also common sense. Marriage partners have enough challenges these days without being divided on spiritual matters. A spiritual tug-of-war can develop between husband and wife, decisions about the spiritual upbringing of children can be divisive and the children receive conflicting messages about faith and life. But the context of the passage does not support an absolute prohibition against “mixed” marriages, and none of the Ten Commandments prohibit such unions.
So, in freedom, a believer could marry a non-believer. I have seen examples of such marriages where God has worked through the believing spouse to bring the non-believer to faith. I have also seen situations where that has not happened. And there are also marriages where the believer has wandered away from what was once a devout faith after a marriage to a non-believer. And even when two sincere Christians marry, there is no guarantee that one of them will not walk away from their faith at some point in the future.
In summary, I think that it is a good idea for a person to try to make sure that the one they are considering for a potential marriage partner is on the same page as they are on spiritual matters (and other major issues as well).