Scholars of all times have returned again and again to struggle with this phrase. On the one hand it does seem at first sight to qualify in some way Christ’s general prohibition of divorce. On the other hand the context makes it clear that Christ considered a divorced person still bound by the marriage bond: To attempt marriage with another would be “adultery.” If there is to be any solution to the dilemma, some alternative translation must be found for one or the other of the three words which appear in our text as “divorce,” “except,” and “fornication” . . .
It is the third word, “fornication,” that perhaps provides the most satisfying solution to the problem. The solutions based on the other two words unconsciously make this word equivalent to “adultery,” without allowing for the fact that when the text speaks of the adultery of the divorced husband or wife, it uses an entirely different word. It would seem that “fornication” refers to something else. Can we discover its exact meaning by looking to see how it is used elsewhere in the New Testament?
The Greek word porneia that is used in Matthew 5 and 9 is in fact both more general and more specific in meaning than the English word “fornication.” In itself it means simply “impurity” (the English word “pornography” which is taken from it has a similarly wide meaning) and the context must decide what precise impurity is being referred to. Such a context is provided, for instance, by St. Paul in his first letter to Corinth, where he condemns the illicit union between a Christian and his dead father’s wife. This he calls porneia (1 Cor. 5:1). The Council of Jerusalem in Acts 15 uses the word in exactly the same sense when it directs Christians of Gentile origin to respect the susceptibilities of their brethren of Jewish origin by complying, where necessary, with Jewish custom in the matter of porneia. The Council had made it clear that, in principle, the Christian is no longer bound by the ritual laws of the Old Testament (Acts 15:7-19). But charity demanded that, where converts from Judaism were in a majority and continued to live according to these ancestral laws, the Gentile Christians among them should make a communal life possible by respecting their social taboos in the matter of idolothytes (food which had been offered in pagan sacrifices), porneia (marriage within forbidden degrees), “blood,” and “things strangled” (non-kosher meat) (Acts 15:20). Exactly the same four concessions had for centuries been demanded of any stranger who wished to make his home in Israel (Lev. 17:8–18:26).
These two examples make it possible, if not likely, that porneia, as well as bearing the generic meaning of impurity, had in certain circumstances the technical meaning of marriage within certain degrees of kinship forbidden by Jewish law. Among the Gentiles there was no restriction on the matter, and marriage between near relatives was not unusual. But it was the Jewish custom which was eventually taken over by the Church, where a marriage of this kind was regarded as being one in name only and in reality as illicit a union as plain fornication. The use of the same word porneia in the context of a dispute about marriage makes it at least possible (more and more scholars today think that it is certain) that the text of Matthew 5:32 and 19:9 refers to such illicit unions and excepts from the general law of indissolubility those “marriages” which were already null and void through forbidden degrees of kinship. The text then could be paraphrased: “If anyone divorces his wife, he may not marry again, except when his marriage was not a real one at all, but had only the appearance of one.”