The Great Commentary of Cornelius à Lapide
1 Corinthians 7:15
But if the unbelieving depart, let him depart. If the unbeliever seek for a dissolution of the marriage, or will not live with his partner without doing injury to God, by endeavouring to draw her way to unbelief or to some wickedness, or by uttering blasphemy against God, or Christ, or the faith, then, as Sanchez lays down from the common consent of the Doctors of the Church (vol. ii. disp. 74), he by so acting is rightly regarded to wish for a separation; then let the unbeliever depart from the unbelieving, because it is better, says S. Chrysostom, to be divorced from one's husband than from God.
Observe that the Apostle in this case allows a separation, not only a toro but also a vinculo; and therefore the believer may contract another marriage, this being a concession made by Christ in favour of the faith; otherwise a Christian man or woman would be subject to slavery. For it is a grievous slavery to be bound in matrimony to an unbeliever, so as not to be able to marry another, and to be bound to live a life of celibacy, even if the unbeliever depart. So S. Augustine (de Adulter. Conjug. lib. i. c. 13), S. Thomas, and S. Ambrose, who says: "The marriage obedience is not owing to him who scoffs at the Author of marriage, but in such case remarriage is lawful."
Further, many doctors, cited by Henriquez (de Matrim. lib. xi. c. 8), amongst whom is S. Augustine (de Adulter. Conjug. lib. i. c. xix.), gather from this verse and from verse12 that the believer whose unbelieving partner is not willing to be converted, even though he may be willing to live with her without injury to God, has by this very fact a right to enter upon a new marriage. But S. Paul and the Canonical decrees (cap. quanto, cap. Gaudemus, tit, de Divort, and cap. Si Infidelis 28, qu. 2) only deal with the case where the unbeliever wishes to depart, or where he is a blasphemer against the faith. And, therefore, other doctors, cited by Henriquez, think that in this case it is lawful for the believer to marry again. And this opinion is the more sound not only for the reason given above, but also because the Fathers who support the first opinion rely on glosses on the various capitula, which are merely glosses of Orleans, and if anything darken the text.
Moreover, no gloss by itself can be the foundation of a right, or of a new law. Since, therefore, it is agreed that the marriage of unbelievers is true marriage, and that it is not dissolved by the conversion of either party, because there is no law of God or of the Church to dissolve it, it follows that they must hold to their contract, which by its very nature is indissoluble. This is strengthened by the consideration that each party possesses good faith; therefore it cannot set aside, unless it is agreed that either or both have no right to this marriage, or that one loses his right through the conversion of the other. This, however, is not agreed on, but is highly doubtful. In matters of doubt the position of the possessor is the stronger, and he ought not to be ousted from it because of any doubt that may arise.
Nevertheless, Sanchez adds (disp. 74, Numbers 9) that it is lawful for the believer to marry again, because it is now forbidden by the Church to live with an unbeliever who will not be converted, because of the danger of perversion which exists nearly always. The unbeliever is then looked upon as having departed, because he refuses to live with the believer in a lawful and proper manner. But Sanchez means that the Church now forbids in general a believer to continue to live with an unbeliever. But this is denied by Navarrus and others; for though the Fourth Council of Toledo forbids a believer to live with an unbeliever if he is a Jew, this was done merely because of the obstinate tenacity of the Jews to their creed. Neither here nor elsewhere is marriage with a heathen forbidden.
Moreover, the Council of Toledo was merely local, and this same canon has been differently interpreted by different authors, as Sanchez says (disp. 73, Numbers 6). And in truth it would be hard and a just cause of offence if, in India, China, and Japan, when the faith is first preached, Christians should be compelled to put away the wives that they had married when unbelievers, or if wives should be compelled to leave their husbands who were unwilling to be converted to Christianity, especially when they were in high position; for occasion would be taken from thence to exterminate Christians and their faith. The case is different in Spain and amongst Christians, where the Church might, without causing scandal, enact this, either by a general law (which as a matter of fact does not exist, as I have said), or by use and custom, by forbidding individuals in particular to remain in marriage with one that was not a believer, because of the danger of perversion. Such a precept it would be the duty of the believer to obey, and therefore it would not be he that was in fault, but the unbeliever, who, by refusing to live in marriage, according to the law binding on the believing partner and the precept of the Church, becomes the cause of the separation. By so acting, the unbeliever will be reckoned to wish for separation, and consequently it would be lawful for the believer to contract another marriage, as Sanchez learnedly argues. For example, Queen Cæsar, wife of the King of the Persians in the time of the Emperor Mauritius, fled secretly to Constantinople, and was there converted and baptized. When her husband requested her to return, she refused to do so unless he became a Christian. He when went to Constantinople and was there baptized, and assisted out of the font by Augustus, and having received his wife again, he returned joyfully to his home. This happened about the year 593, as Baronius related on the authority of Paul the Deacon and Gregory of Tours. All that has been said must be clearly understood to refer to matrimony contracted when both partied are unbelievers, followed by the conversion of one and the refusal of the other to be converted; for matrimony contracted by an unbeliever with a believer has been declared null and void by the Church since the time of S. Paul and thence it is that difference of faith is a barrier to matrimony. This was the reason why Theresa, sister of Adelphonsus, King of Liège, refused to marry Abdallah, King of the Arabs, unless he adopted the Christian faith. This he promised, but falsely. Therefore on the arrival of Theresa he forced her, in spite of her struggles; but being smitten by God with a sore disease, he was unable to be cured without sending back Theresa to her brother. This is told by Roderic, Vazæus, and Baronius (A. D. 983).
S. Eurosia too, daughter of the King of Bohemia, having been taken prisoner by the King of the Moors, chose death rather than marriage with him; and while she was patiently awaiting the sword of the executioner, she heard an angel saying, "Come, my elect, the spouse of Christ, receive the crown which the Lord hath prepared for you, and the gift that your prayers shall be heard as often as the faithful call upon you for help against rain or any storm whatsoever." Having heard these words, her arms and legs having been lopped off, she gave up the ghost, being renowned for her miracles, as Lucius Marinæus Siculus related (de Rebus Hispan, lib. v.).
But God hath called us unto peace. Peace of conscience with God, and of agreement with men. Therefore, on our part, let us not depart from unbelieving husbands, but live with them as peacefully as we can. Secondly, and more fitly, peace here stands for that rest and tranquil life to which the Apostle is urging the married believer. Such a life in separation and solitude is to be preferred to marriage with an unbeliever who wishes to depart, and who is perpetually provoking the believer to quarrel, and disturbing his peace. This better agrees with the mention of departure which has gone just before these words, and of which I shall have more to say.