It seems that Paul had been asked, "When only one person in a marriage believes in Jesus, should they divorce the other?" The apostle answered, "No!" If the unbelieving spouse is willing to stay, there is no way that the gospel or the church should force them apart. Indeed there is something very special to God about a family when even one person belongs to Christ, because He longs to share His grace with the entire household (Acts 2:39).
 
That does not mean that all the family are saved through the faith of one person: each person is individually accountable before God and each needs to come to Him in repentance and faith. But the privilege of having a believer in the family is very great (Romans 11:16). Joseph's presence blessed Potiphar's household (Genesis 39:5) in the same way that Jacob's godly devotion benefitted his Uncle Laban (Genesis 30:27). The opportunity to see God at work in a believer's life is a glimpse of God's kingdom, which is designed to attract others to put their trust in Jesus (1 Peter 3:1-2).
 
However, some spouses might have been so captivated by their pagan practices that the Spirit of Christ in their partner repelled them, precipitating divorce. In that case, Paul said, the believer should not force them to stay. If they reject the loving blessing of the Lord, they cannot be forced to welcome Him or His children. But the principle remains that it is God's intention for the gospel to be infectious: the family and workplace are natural environments for the seed of the gospel to be sown and be life-changing.
 
We should never say that we know somebody will never be interested in Jesus or want to be saved. How could we ever presume to know what the Lord will do through our godly witness? Our task is to live in the strength that Christ gives, in front of the unbelievers in our families, communities and workplaces. As we do that, He will be at work in those who witness our integrity of life, devotion to the needs of others, hear the gospel and listen to the answers we give to their questions (1 Peter 3:15). God does not want anybody to perish (2 Peter 3:9) and will use your sanctified lifestyle and gospel words to win some of those close to you, into His kingdom.