Marriage and Virginity
As you say, "That is what the Lord orders, the apostle teaches, and both Testaments command." Who would deny, however, that it is different when it does not concern two persons getting married, but persons already married? When they married, both shared the same lack of faith; but after the gospel was preached, one of them came to believe and the other did not. So, if this case is different, which is clear beyond any shadow of doubt, why did not the Lord, as well as the apostle, also command the believer to stay married to the unbeliever? Was it perhaps to give the opportunity for what the apostle claimed so confidently: Do you want proof that it is Christ who speaks in me (2 Cor 13:3)? And certainly
Christ is the Lord. Do you follow what I am saying? Or do I have to dwell longer on it and explain it in more detail?
26. Pay attention, and let me present it for your consideration in more explicit language.
Consider two married people, both in the same state of unbelief, just as they were when they married. That command of the Lord, teaching of the apostle, and commandment of the Old and New Testaments, whereby a believer is forbidden to enter a union with an unbeliever, has nothing to do with them. They are already married, and both are still unbelievers; they are still the same as they were before they were married, and the same as they were when they married. Then someone comes preaching the gospel, and one of them comes to believe; but the one without the faith agrees to stay with the one who believes. Does the Lord command the one who believes to divorce the one who does not believe, or does he not command this?
If you say, "He commands it," the apostle cries out, I say it, not the Lord (1 Cor 7:12); and if you say, "He does not command it," I want to know the reason. Do not give me the answer you gave in your letter: "Because the Lord forbids the faithful to be united with unbelievers."
That is no reason at all here, when we are not talking about persons entering into a union with each other, but persons already in that union. If, therefore, you yourself do not find any reason why the Lord does not forbid what the apostle forbids (for I think you see now that there is not the reason you thought there was), then see whether perhaps the reason is the one that appeared to me as the one to put forward then, and the one that must now be defended. It is that we have to understand that the Lord states what he recognizes justice to require as absolutely obligatory, and that is what he commands or forbids, so that it is absolutely wrong to act differently. On the other hand, when he leaves something to free choice, so that it is not wrong either to do it or not do it, he himself leaves it open for his servants to give advice, in favor of what they see as the good thing to do.