By Timothy Sparks
Paul says, “if the unbeliever separates himself, he is to separate himself” (1 Cor. 7:15).1 Jesus says, “Therefore what God united, a human cannot divide” (Mt. 19:6; Mk. 10:9). While the unbeliever is able to separate the “who” (“himself”), he is not able to separate the “what.”
It is interesting that Jesus says, “what” (Mt. 19:6; ὃ, neuter singular). The Pulpit Commentary has it correct–“neuter singular, not ‘those whom,’ plural and concrete, that he may make it clear that he is here speaking in the abstract, not specially of Adam and Eve. What he enunciates is true of all wedlock, not simply of the case of our first parents. Let not man put asunder. Man does thus infringe the primitive rule when he divorces his wife. Herein he opposes God and acts against nature. He and his wife are one; they can no more separate from one another than they can from themselves. If we regard our Lord’s language in this passage without prejudice, and not reading into it modern notions, we must consider that he here decrees the indissolubility of the marriage tie. His hearers plainly understood him so to speak, as we see from the objection which they urged” (http://biblehub.com/commentaries/pulpit/matthew/19.htm).
Paul addresses the situation in which the unbeliever separates himself. If the unbeliever separates/departs, the believer is not “enslaved” [δουλόω (douloō)] to leave/depart with the unbeliever (1 Cor. 7:15). Paul uses the perfect tense, indicating that the believer was not and currently is not (never has been) enslaved to the unbeliever. While marriage is for life (Rom. 7:2; 1 Cor. 7:39), husband and wife are not “enslaved” to each other (1 Cor. 7:15).
There is no favorable approval for the believer to initiate divorce either with a believing spouse or with an unbelieving spouse, seen by the two specific words used for both “separate/divide” [χωρίζω (chōrizō)] and “abandon/leave” [ἀφίημι (aphiēmi)] (1 Cor. 7:10-15). If the unbelieving spouse leaves, there is also no favorable approval for the believer to marry another. Jesus explicitly and consistently states, “and marries another commits adultery” (Mt. 19:9; Mk. 10:11-12; Lk. 16:18).
1Unless otherwise stated, translations are mine.