I’ve not seen this point in any of the discussions about Amoris Laetitia, specifically the section that allows, in some limited cases, reception of holy Communion by the divorced and remarried. It is a solid theological argument, based not only on the current guide for confessors issued by the Holy See, called the Vademecum , but also the writings of Saint Alphonsus Liguori on the Sacrament of Penance.
In some cases, when the penitent is guilty of an objective mortal sin (an act that is gravely immoral, but which lacks the full knowledge and full deliberation of actual mortal sin), but is unaware of the gravity or immorality of the act, the confessor is advised by the Church and by Saint Alphonsus (and many other authors following his opinion) NOT to make the penitent aware that his act is a grave sin. For then an act that is only material sin, might become formal sin (i.e. an objectively grave act might become actual mortal sin).
In such cases, the penitent is given valid absolution in the Sacrament of Penance and is permitted to receive holy Communion, even though his confessor knows that he is continuing to commit an objective mortal sin in his life!! And this theological position is at the very least the common opinion of moral theologians,
“The principle according to which it is preferable to let penitents remain in good faith in cases of error due to subjectively invincible ignorance, is certainly to be considered always valid, even in matters of conjugal chastity. And this applies whenever it is foreseen that the penitent, although oriented towards living within the bounds of a life of faith, would not be prepared to change his own conduct, but rather would begin formally to sin.” 
This passage is followed by a series of paragraphs which place this principle in its proper perspective. The document speaks of the “law of gradualness” and cautions the confessor not to deny absolution (and by implication Communion) even to persons who frequently relapse into the same sin.
The first point is that the Church has, for centuries, permitted persons who were guilty of objective mortal sin to receive Communion, as long as they were not guilty of actual mortal sin (as far as the penitent alone, or the penitent and confessor together might be able to judge this). This establishes the principle that a person guilty of objective mortal sin, but not actual mortal sin, may generally receive Communion.
Only actual mortal sin deprives the soul of the state of grace. And the state of grace is the main requirement for a Christian to receive holy Communion. Other requirements are established by the Church’s authority, and made stricter or looser as the Roman Pontiff and an Ecumenical Council might decide. But to be a Christian in the state of grace is the foundation of any larger set of criteria for reception.
The second point is that the Vademecum permits absolution even when a penitent repeatedly, even frequently, falls into the same grave sin. “Frequent relapse into sins of contraception does not in itself constitute a motive for denying absolution” . And this repeated absolution implies a repeated worthiness to receive Communion.
The third point is that the Council of Trent permits a priest who is cognizant of actual mortal sin to receive Communion, prior to Confession, if he repents with perfect contrition and no other priest is available for Confession at the time . Actual mortal sin with perfect contrition restores the state of grace. So again, the sinner is permitted to receive Communion because he is a Christian who is reasonably believed to be in the state of grace. (The whole moral law is open to reason. A baptized Christian cannot be certain he is in the state of grace, but he can make a reasonable determination as to the likelihood.)
Applying these three points to the divorced and remarried is not so complicated. If the spouse-penitent is striving to conform to Church teaching, but frequently falls into the sin of sex outside of a valid marriage, he or she may confess and receive Communion.
In other cases, the penitent might be guilty of unrepentant objective mortal sin, which is not an actual mortal sin due to a lack of full knowledge of the Church’s teaching on divorce and marriage. And knowledge here is not merely the reception of information on what the Church objectively teaches, but the subjective understanding and acceptance of the teaching by the conscience. So the spouse in this case is more like a penitent afflicted by “subjectively invincible ignorance”, and may not be guilty of actual mortal sin, despite knowing the Church teaching as a matter of fact.
On the third point, the divorced and remarried penitent is not a priest who must say Mass, so the teaching of Trent does not apply in and of itself. Rather, a theological argument can be made that if a priest who knows he has committed an actual mortal sin may receive Communion, after repenting with perfect contrition, this proves that the Church possesses the authority to give Communion to Christians in the state of grace, despite grave sin. If some of the divorced and remarried are in the state of grace, despite objectively grave sins, the Church has the authority to give them Communion.
My personal preference for Communion discipline is much stricter. I would like to see a general rule, with exceptions for grave circumstances, that prohibits Communion in cases of mere objective mortal sin, even without full knowledge or full deliberation. But Pope Francis is Peter, and Peter holds the keys. I support Pope Francis, just as I support Peter himself and all of his successors.
Ronald L. Conte Jr.
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 Pontifical Council for the Family, “Vademecum for Confessors Concerning Some Aspects of the Morality of Conjugal Life”
 Vademecum, 3, 8.
 Vademecum, 3, 5.
 Council of Trent, Decree on the Eucharist, Chap. VII