It happened that it was a Catholic doctor, a Father of the Church, no less, who identified several facts that he imputed to the Blessed Virgin as imperfections: during the finding of the Child Jesus in the Temple, and also at Cana. It was St. John Chrysostom.
On the contrary, it must be said that the Most Holy Virgin never committed the least imperfection. The reasons explaining this are numerous.
First because the Mother of God did not have the “source of sin” – also called concupiscence – which is one of the principal causes of imperfections. This absence is linked to her immunity from original sin.
Moreover, the Virgin of virgins possessed perfect virtue through the grace that had been given to her. She was also destined to be a model of holiness, because Our Lady is the first of the redeemed: it is fitting that she who has primacy in the order of holiness should realize it in her consummate perfection.
Finally, her perfect prudence always determined her activity in the way that was most conformed to the will of God.
This is why St. Thomas Aquinas did not hesitate to say that St. John Chrysostom went too far in his writing. And while St. Pius V had the works of the great doctor republished, he requested that the incriminating passages not be included.
The Mother of God possessed impeccability
But the greatest reason explaining the absence of sin and imperfections in Mary is that she was impeccable.
The Council of Trent, in Session VI, Canon 23, affirms: “If anyone shall say that … throughout his whole life [a man] can avoid all sins even venial sins, except by a special privilege of God, as the Church holds in regard to the Blessed Virgin: let him be anathema.”
For his part, St. Thomas admits confirmation in grace, out of suitability for the Mother of God. Impeccability consists in being unable to sin, because of an interior capacity. It is distinguished from confirmation in grace, which is maintaining the state of grace until death, in other words, not committing mortal sin: this grace can be explained by external help from God. But impeccability requires an inner cause in the subject that prevents sin.
This is clearly the case of the Incarnate Word, Jesus Christ: it is an impossibility that the divine person would commit a sin. In the case of the man-God, the beatific vision and perfect virtue are added to the divine personality.
Impeccability exists to a lesser degree in the blessed: inundated by the light of glory they can no longer sin. It would be impossible to possess the beatific vision and sin.
To an even lower degree, impeccability comes from the very great difficulty to sin which results from the gift of a special grace. This inclines a person so much to the good that it is almost impossible to break away from it. God added a special assistance for His Mother which removed the causes of sin.
In this way, the Mother of God was impeccable, that is, she could not sin, through her perfect virtue, through her confirmation in grace, and through a special assistance from God.
This doctrine allows for a deeper penetration into these magnificent words of Pope Pius IX in Ineffabilis Deus: “so wondrously did God endow [the Virgin Mary] with the abundance of all heavenly graces poured from the treasury of His divinity, that she, ever absolutely free from every stain of sin, all fair and perfect, would possess that fullness of holy innocence and sanctity that no one, under God, can conceive of anything greater, and which no one, except God Himself, can ever measure the greatness.”