To the married I give this command (not I, but the Lord): A wife must not separate from her husband. But if she does, she must remain unmarried or else be reconciled to her husband. And a husband must not divorce his wife.
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."
Marriage Counseling 101
#2 Because of their desire to serve Christ, some people in the Corinthian church thought they out to divorce their pagan spouses and marry Christians. Paul affirmed that God's ideal is for marriages to stay together - even when one spouse is not a believer.
#3 God regards the marriage as "sanctified" by the presence of one Christian spouse. The other does not receive salvation automatically, but is helped by their relationship. The children of such a marriage are to be regarded as holy until they are old enough to decide for themselves.