1 Corinthians 7:12 But to the rest speak I, not the Lord: If any brother hath a wife that believeth not, and she be pleased to dwell with him, let him not put her away.13 And the woman which hath an husband that believeth not, and if he be pleased to dwell with her, let her not leave him.14 For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband: else were your children unclean; but now are they holy.
Here in 12 and 13 Paul is saying that if two are married and one is a believer and the other is not then they should stay together. The word teaches we should not be unequally yoked, meaning a believer an a non believer but if they are they should work to stay together and hope the unbeliever becomes a believer. Verse 14 lets us know that because there is one believer in the marriage that there is an umbrella over the family for the blessings of God. This could lead to the unbeliever to come the salvation of Christ. One Christian in a marriage brings grace that spills over on the spouse. The presence of even one Christian parent will protect children from undue spiritual harm and they will receive many blessings, and often that includes salvation.We all probably know of situations like this and we need to pray for these families that the one believer stays strong and God grants the them rest of their family through salvation.