1 Corinthians 7:12

But to the rest say I, not the Lord: If any brother hath an unbelieving wife, and she is content to dwell with him, let him not leave her.

Say I, not the Lord ... The meaning here is not that Paul's injunction here had any less inspiration and authority behind it, but that its authority derived from his own apostolic commission, and not from any direct commandment uttered by Jesus during his ministry, such as that he had just cited. There is not the slightest disclaimer here of full and absolute authority for what Paul commanded in the Spirit of God. As Marsh expressed it, "In this instance Paul cannot refer to any direct command of Christ, as he could for the previous case; but his words carry the full weight of inspiration and authority."[23] One must deplore the blindness of many commentators on this exceedingly important point.

Jesus' teaching on marriage was directed to the Jews who were all in covenant relationship with God; and his words had no application at all to mixed marriages which Paul dealt with here; hence the necessity for Paul to issue the command himself in the fullness of his apostolic authority. How easy it would have been for him to attribute some saying to Jesus on this, instead of assuming full responsibility for it himself; but, in the light of his example, we may be sure that no apostle ever did such a thing. How vain, therefore, are the speculations of a certain school of critics who accuse the apostles of attributing to Jesus words which were, in fact, their own deductions and not the words of the Lord. Paul's distinguishing such things in this verse is an overwhelmingly powerful testimony to the truth of the entire New Testament.

This verse through 1 Corinthians 7:16 deals with the problem of divorce in mixed marriages, that is, marriages between Christians and pagans, a situation which arose, not from Christians marrying pagans, but from the conversion of one out of a pagan couple. Paul's command here is that the marriage stands, unless the unbeliever is unwilling and will not allow it to stand.