Marriage and Virginity
it is permitted to separate from a husband or wife because of an act of adultery, how much more detestable in a husband or wife is adultery of the spirit, in other words lack of faith!†8
Scripture says of this, See how those who distance themselves from you will perish; you have destroyed everyone who is unfaithful to you (Ps 73:27).
The Apostle Discourages What the Lord Allows
18. It is permitted [to divorce an unbelieving spouse], but it is not good to do, because people might take offense at the breakup of marriages and abhor the very doctrine of salvation that forbids the things that are not permitted. They would then continue on in the same state of unbelief, worse than before and destined to perish. For this reason the apostle intervenes with the advice forbidding us to do what is permitted though not good. While the Lord does not forbid the faithful, men and women, to leave husbands or wives who are not believers, at the same time he does not command them to do so. If he did command it, the apostle's advice not to act in that way would be out of place. The Lord's faithful slave would never forbid doing what the Lord commands us to do.
20. On one occasion, through the prophet Ezra, the Lord did command this and it was done.
Those of the Israelites who were still able to keep foreign wives divorced them.†9 What was happening was that, instead of the wives being won over to God through the influence of their husbands, the husbands were being seduced to the worship of alien gods through their wives' influence. The great grace of the savior had not yet begun to spread its light, and for the most part those people were still yearning for the material benefits promised in the Old Testament. Therefore, when they saw that even people who worshiped a multitude of false gods were rich with the earthly goods they were looking to receive as a special favor from God, they were won over by the sweet wiles of their wives, first of all to being in awe of those false gods, and then to taking part in the worship of them.
Because of this God had given the commandment through Moses that no one was to marry a foreigner.†10 Quite properly, then, in obedience to the Lord's command they divorced the wives they had married in disobedience to the Lord's command. When, however, the gospel began to be preached to the Gentiles, it came upon a situation where Gentiles were already married to each other. In these cases, if both did not accept the faith, but one or the other did, provided the one who did not believe agreed to live with the one who did, it was not proper