1 Corinthians 7:10

In this paragraph the apostle gives them direction in a case which must be very frequent in that age of the world, especially among the Jewish converts; I mean whether they were to live with heathen relatives in a married state. Moses's law permitted divorce; and there was a famous instance in the Jewish state, when the people were obliged to put away their idolatrous wives, Ezr 10:3. This might move a scruple in many minds, whether converts to Christianity were not bound to put away or desert their mates, continuing infidels. Concerning this matter the apostle here gives direction. And, I. In general, he tells them that marriage, by Christ's command, is for life; and therefore those who are married must not think of separation. The wife must not depart from the husband (Co1 7:10), nor the husband put away his wife, Co1 7:11. This I command, says the apostle; yet not I, but the Lord. Not that he commanded any thing of his own head, or upon his own authority. Whatever he commanded was the Lord's command, dictated by his Spirit and enjoined by his authority. But his meaning is that the Lord himself, with his own mouth, had forbidden such separations, Mat 5:32; Mat 19:9; Mar 10:11; Luk 16:18. Note, Man and wife cannot separate at pleasure, nor dissolve, when they will, their matrimonial bonds and relation. They must not separate for any other cause than what Christ allows.

— Matthew Henry's Concise Commentary (public domain)

not I, but the Lord--(Compare Co1 7:12, Co1 7:25, Co1 7:40). In ordinary cases he writes on inspired apostolic authority (Co1 14:37); but here on the direct authority of the Lord Himself (Mar 10:11-12). In both cases alike the things written are inspired by the Spirit of God "but not all for all time, nor all on the primary truths of the faith" [ALFORD]. Let not the wife depart--literally, "be separated from." Probably the separation on either side, whether owing to the husband or to the wife, is forbidden.

— Jamieson-Fausset-Brown Commentary (public domain)