Baptist Greek scholar A.T. Robertson also prominently mentioned the same textual theory in his comments on Matthew 19:9 and 5:32 (although he himself disagrees with it):
Here, as in 5:31 f., a group of scholars deny the genuineness of the exception given by Matthew alone. McNeile holds that “the addition of the saving clause is, in fact, opposed to the spirit of the whole context, and must have been made at a time when the practice of divorce for adultery had already grown up.”
McNeile denies that Jesus made this exception because Mark and Luke do not give it. He claims that the early Christians made the exception to meet a pressing need. . . . . . (Robertson, I, 155, 47)
The Oxford Dictionary of the Christian Church allows for more possibility that this was indeed the case:
[T]he Lord . . . abrogated the Mosaic toleration of divorce (Mt. 5:31 f., 19:3-9; Mk 10:2-12; Lk 16:18) and condemned remarriage. The “Matthean exception” permitting remarriage (19:9), which conflicts with the other Gospels, the rest of the NT and the general tradition of the Western Church, is perhaps to be understood as an early gloss to render the Christian law easier. (Cross, 889)
To summarize this at-times confusing material: according to the several reputable Protestant reference sources surveyed here, a significant number of Bible scholars hold that Jesus’ recorded teachings concerning divorce in Matthew contradict His teaching in Mark and Luke because of the “exception clause” in Matthew. Some, therefore, have concluded that this clause was a later addition to the actual inspired biblical text. Also, some of these sources concede that the “strict interpretation” of St. Paul’s teaching on divorce was held for the first eight hundred or so years of Church history.
One must be very careful, if taking this textual approach, not to deny biblical infallibility and inspiration. If it can be demonstrated that a portion of the text was not actually in the Bible in the first place (an interpolation, or textual error, or text only in late manuscripts, such as Mark 16) then this poses no problem for inspiration. But if it is part of the Bible, it must be synthesized with the rest of the Bible in a harmonious whole, and cannot be contradictory.
The fascinating thing in the above citations is that the problem comes up at all. Obviously, people were concerned about an alleged contradiction or a vexing hermeneutical difficulty, because they thought it was so clear that Jesus and Paul did not allow exceptions, except in Matthew, where the text is then questioned as a later addition. In other words, the Bible is not so crystal clear and self-interpreting as Protestants are wont to believe. And perhaps the “strict” Catholic view concerning marriage and divorce is not as utterly unfounded as many are led to believe.
The eminent Protestant Bible scholar James Dunn goes further; in fact too far, if his position is that the apostle Matthew himself deliberately altered received Christian tradition: up to and including the very sayings of Jesus, and thus contradicted inspired Scripture elsewhere. This is unacceptable and must be deemed as an erosion of a high, inspired view of Holy Scripture; nevertheless, it is helpful to elucidate the controversy over how Matthew 19:9 can be harmonized with the other passages to arrive at a coherent viewpoint on marriage and divorce:
Some sayings have been interpreted differently in the course of transmission . . . We must note also how some sayings of Jesus have been deliberately altered in the course of transmission – altered in such a way as to give a clearly different sense from the original . . . Note also the way in which Jesus’ clear cut verdict against divorce preserved in Mark 10.11 has been softened by the addition of the unchastity clause in Matt. 19.9 . . .
[T]he unconditional ruling of Jesus in Mark 10.11 is amended by Matthew to allow the possibility of divorce in cases of unchastity. (Dunn, 73-74, 247)
Moving from biblical teaching to the history of Christian teaching throughout the centuries, we find that the early Church took a very “strict” view of divorce and remarriage, which is a relevant consideration for the many Protestants who see themselves as hearkening back to the beliefs and practices of the early Christians. In his book about the first five centuries of the Church, Early Christianity, Protestant historian (and famous Luther biographer) Roland Bainton stated, “Second marriages were not permissible unless the first partner died prior to the baptism of the survivor” (p. 56).
The Catholic Encyclopedia provides an overview of Sacred Tradition on the question:
The testimonies of the Fathers and the councils leave us no room for doubt. In numerous places they lay down the teaching that not even in the case of adultery can the marriage bond be dissolved or the innocent party proceed to a new marriage. They insist rather that the innocent party must remain unmarried after the dismissal of the guilty one, and can only enter upon new marriage in case death intervenes. (Herbermann, V, 56-57)
That article goes on to document this view from numerous patristic sources, including the Shepherd of Hermas, Justin Martyr, Athenagoras, Tertullian, Clement of Alexandria, Basil of Cæsarea, John Chrysostom, Theodoret, Ambrose, Jerome, and Augustine.
The leading magazine of Evangelical Protestantism, Christianity Today(founded by Billy Graham), confirms these beliefs of the early Church. Michael Gorman, in his article entitled, “Divorce and Remarriage From Augustine to Zwingli” (December 14, 1992) wrote:
In the early church, many voices addressed the subjects of marriage, divorce, and remarriage, but their message, on the whole, was quite unified. Christian marriage, they said, is an indissoluble bond. Divorce, with the implicit right of remarriage, was not an option for Christian couples (though Origen admits some toleration existed), but permanent separation was. Remarriage after separation was considered punishable adultery or bigamy . . .
Luther and Calvin allowed divorce on a number of grounds, but historically, many Protestant denominations and individuals have been stricter in their beliefs and practices concerning divorce. In Protestant churches today, however, there are ever more permissive attitudes towards divorce and remarriage. This goes far beyond the teaching of the Bible itself (even if one accepts an “adultery clause”) and is another instance of the decay of biblical orthodoxy and traditional Christian morality among many Protestants.
[Footnote 6] It must also be noted that individual Catholics have also fallen prey to the cultural watering down of strictly interpreted marriage vows and traditional Christian opposition to divorce, and statistically, they divorce at nearly the same rates as the rest of society. Official Catholic teaching on the indissolubility of marriage, however, has never wavered; furthermore, statistics also show that regular churchgoing Catholics divorce at a much lower rate.
[from my original manuscript but not included in the published edition of the book] Too often, Catholics marry outside the Church or they enter into “second marriages” without the benefit of an annulment (a declaration that the proper conditions for a valid, sacramental marriage were not present from the beginning). It is also almost certainly true that some annulments being granted are done without proper cause. The process is likely being abused, because the numbers of annulments in the United States have so greatly increased. On the other hand, as Catholics understand less and less what is involved in a sacramental, Catholic marriage, it is more likely that annulments will increase, because of that very ignorance.