"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."
Paul is here giving some brief answers to questions written to him by the Corinthian believers (verse 1). Apparently a new convert was troubled over the matter of having a heathen companion. Would it desecrate the marriage, thus making it better to separate? Also, what about the children? Would they be defiled by the division in the home?
Paul's counsel was not to separate if the unbelieving companion wanted to preserve the home. "For the unbelieving husband is sanctified by the Wife, and the unbelieving
wife is sanctified by the husband." Verse 14. Obviously Paul did not mean that the heathen companion would be automatically saved by staying with the Christian spouse, but rather that the marriage status was not desecrated by the heathen alliance--it was still a valid union.
Then Paul adds, "Else were your children unclean; but now they are holy." He was clearly saying that if a divorce were granted on the basis of the marriage itself having been improper, then the children would have to be considered illegitimate, or "unclean." But, no, Paul says the union is holy and therefore the children are "holy" in the sense that they are legitimately born.
Some have assumed that only the children of two believing parents can be saved. But Paul is not talking at all about the salvation of the child. The words "holy" and "sanctified" have the same root meaning, and if the child could be saved, then the heathen parent, being "sanctified" by the Christian spouse, would also be saved. The advice is simply this: don't let religious differences break up an already-established family. It does not affect the status of the marriage before God.