From the oceans of ink spilt on this subject (Mt 5:32 and 19:9) I have attempted to distil the two most common Catholic interpretations:
Clas (Classical). The ‘exception’ clause refers to reasons for separation, not remarriage, which apart from rare cases (the Pauline Privilege etc.) is neither licit nor even valid until the death of one party.
Mod (Modern). The ‘exception’ clause refers to pseudo marriages (eg within forbidden degrees of kinship).
Sad to say, in my experience of modern Scripture scholarship which is purportedly Catholic, the exception proves the rule: it is an absolute minefield of nonsense and heresy. Many of these vagaries have been reprobated, explicitly or implicitly, in Magisterial documents for well over a century. One extremely common tendency of latter-day technical Scripture scholars (working from the biblical languages etc.) is to say ‘the passage means X – and nothing else’.
So often, X is in conflict – many times avowedly so! – with how the Church has read the text since time immemorial.
Even a cursory acquaintance with traditional interpretations suffices to show that they seem to be both more Catholic and more catholic. Thus, in addition to being, on the whole, far more respectful both of the Magisterium and of the entire sensus fidei, traditional interpretations are more liberal in the best sense of this word. A classical commentator will often have no problem if one of his colleagues reads the passage differently – provided the variant exegesis is not at odds with the Church in her doctrine or praxis. And why not? Since we are dealing with the Word of God – an infinite Being – why cannot the same text have infinitely many intended meanings? Intended that is by the Primary Author, though not necessarily by the secondary, human authors.
In effect, the Fathers, Doctors of the Church and other traditional exegetes address us somewhat as follows: ‘This is what I have drawn from the Word of God. But if you have found something different, good for you – provided we all stay obedient to the Church’.
When it is a question of the human authors of Holy Writ, the pitfall of eisegesis – reading into the text what is not there – becomes far more likely. So it may be asked: what did Saint Matthew himself have in mind when he penned these two passages? Interpretation Clas? Interpretation Mod? Both? Neither?
The ‘neither’ hypothesis need not detain us here, having a probability of zero or very close to it. (If the Saint did not intend either interpretation, what did he have in mind?) In favour of interpretation Mod it is alleged that Clas divorces Christ from His Church, which has always allowed separation for grave reasons other than adultery (domestic violence and so forth).
Proponents of Clas can, however, reply as follows: in the tradition of the Church, adultery is the only legitimate cause for permanent separation even against the will of one party. With all the other reasons, the grave duty of spouses to live together normally revives as soon as the reason for separation dies (canon 1153 section 2). Whereas in the case of adultery, though the innocent party may take back the guilty one, and this will often be praiseworthy; he or she may even insist – such condonation is not a requirement of justice (canon 1152 section 1).
Irrespective of Saint Matthew’s intentions however, there remains the possibility that, at any rate in the Divine Mind, Mt 19:9, in whatever exact form it came from the Saint’s pen (now probably irretrievable) was intended to express Mod as well as Clas. It could well be that this dual meaning was also intended by the Holy Spirit when the earlier text was inspired.