1 Corinthians 7:16 (ESV)

16 For how do you know, wife, whether you will save your husband? Or how do you know, husband, whether you will save your wife?

If the believing spouse strives for peace in the marriage, there is a strong possibility that the unbelieving spouse will come to faith and be saved. With this message of hope, Paul encourages this third group of people to persevere in their marriages.