Pope Innocent III
On the Bond of Marriage and the Pauline Privilege [From the letter "Quanto te magis" to Hugo, Bishop of Ferrara, May 1, 1199]
405 Your brotherhood has announced that with one of the spouses passing over to heresy the one who is left desires to rush into second vows and to procreate children, and you have thought that we ought to be consulted through your letter as to whether this can be done under the law. We, therefore, responding to your inquiry regarding the common advice of our brothers make a distinction, although indeed our predecessor seems to have thought otherwise, whether of two unbelievers one is converted to the Catholic Faith, or of two believers one lapses into heresy or falls into the error of paganism.
For if one of the unbelieving spouses is converted to the Catholic faith, while the other either is by no means willing to live with him or at least not without blaspheming the divine name or so as to drag him into mortal sin, the one who is left, if he wishes, will pass over to second vows. And in this case we understand what the Apostle says: "If the unbeliever depart, let him depart: for the brother or sister is not subject to servitude in (cases) of this kind" [1 Cor. 7:15]. And likewise (we understand) the canon in which it is said that "insult to the Creator dissolves the law of marriage for him who is left." [from Isaac],
406 But if one of the believing spouses either slip into heresy or lapse into the error of paganism, we do not believe that in this case he who is left, as long as the other is living, can enter into a second marriage; although in this case a greater insult to the Creator is evident. Although indeed true matrimony exists between unbelievers, yet it is not ratified; between believers, however, a true and ratified marriage exists, because the sacrament of faith, which once was admitted, is never lost, but makes the sacrament of marriage ratified so that it itself lasts between married persons as long as the sacrament of faith endures.
1) Quanto te affirms that true marriage does exist among unbelievers, (notwithstanding the fact that they do not regard marriage as indissoluble.)
2) Quanto te affirms that a marriage between believers is "ratified" because of the "sacrament of faith." A ratified marriage remains even if one of the partners should renounce their faith.
3) The Pauline Priviledge is affirmed and the grounds permitting the convert to remarry are expanded to include not only
a) convert who have been deserted by the unbelieving spouse, (as per Paul) but also
b) a convert who would be subjected to blasphemy by an unbelieving spouse who remains, or
c) a convert who would be led into mortal sin by a spouse who remains.
How the unbeliever's blasphemy or drawing to mortal sin amounted to the forteiture of the unbelievers marriage and how these acts were to be proved were not determined by these decretals.
The implication of course was significant: a valid, consummated marriage between Christian and unbeliever was dissoluble.