1 Corinthians 7:14
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. 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.
The unbelieving husband is sanctified by the wife and the unbelieving wife is sanctified by the husband in that the believer's faithful, loving fidelity exerts a sanctifying influence that may draw the unbelieving spouse toward faith and the light. The children of such a union are counted holy rather than unclean. The verse teaches that a believer already married to an unbeliever should remain faithful in the marriage rather than leave because of the unbeliever's faith or opposition, for unbelief alone is not grounds for ending the marriage, but only if the unbelieving spouse chooses to leave. This obligation is strengthened, not lessened, when a person entered marriage while unconverted and later became a believer, and loving and meek fidelity then may influence the unbelieving spouse to believe.
When one spouse accepts the truth and the other opposes it over the Sabbath, the believing wife must not leave her husband merely because he does not keep the Sabbath, but should remain faithful in her duties and, if possible, lead him to the light. At the same time she must not give up her convictions because of his unbelief, for Christ's claims take precedence over family pressure. The same principle that applies to a believing wife applies to a believing husband or child. A wife's sanctified and honorable conduct, preserving her dignity with sincere love for God and her husband, wisdom, patience, prayer, and moral courage, can influence her unbelieving husband toward holiness and spiritual good, and through this influence may help save both him and herself.
The counsel to remain does not make deliberately entering a marriage with an unbeliever acceptable. The verse belongs to the Scriptural rule for marriage, desertion, and remarriage, where parting a man and his wife is a serious matter that must have Scriptural ground. When an unbelieving wife leaves her husband, obtains a divorce from him, and marries another man, the husband who did not leave her is free from the first marriage, and if he then marries again his new union is lawful and should not be disturbed.