Bernard, Thomas, Albert the Great, and Bonaventure were participants in what proved to be a very long and complex theological argument. To boil that argument down, some argued Mary was purified of sin before her soul was infused into her body. Others, like Bernard, et al., insisted she was purified of sin after her soul was infused into her body (but well before her birth).
In the end, a guy named Duns Scotus finally resolved the problem by addressing two questions: 1) Why would God preserve Mary from sin? and 2) How did God do it?
Scotus’ answer as to why God would do this is telling, because it again shows Mary as a) a living commentary on the saving power of Christ who is totally referred to him and b) a kind of icon or archetype of the whole Church, whereby God does first in her what he will one day do for all his saints.
Duns Scotus said that since Christ is a perfect savior, there must be at least one instance of somebody who is perfectly saved by Jesus—saved from top to bottom and from beginning to end— saved so perfectly that they were saved, not by being pulled out of the pit of sin, but by being kept from ever falling in at all. And the fitting candidate for that perfect gift of preventative salvation is Mary:
He who is the most perfect mediator must have a most perfect act Of mediation in regard to some person on whose behalf he exercises the mediatorial office. Now Christ is the most perfect . . . and he had no more exalted relation to any person than to the Blessed Virgin Mary . . . This could not be if he had not merited for her preservation from original sin.( Duns Scotus, Commentarium in Sententiarum, III, 3, 1, 4)
Notice the logic here. The point is not ultimately Mary’s glory, but Christ’s. Mary’s absolutely perfect salvation—a salvation so perfect that sin never got its hooks in her in any way—is a witness to the perfection of Christ’s saving power. It’s a sign of hope to all sinners—even the most wretched—that Christ’s saving power displays complete dominion in any human circumstance.
Note also that it’s fittingness, gauged in relationship to God’s sovereignty, and not some idea of exterior restraints on God, that Duns Scotus has in view here. Mary is a fitting recipient of this singular gift, just as a fine wine is most fitly served in a golden goblet and not a styrofoam cup. I mention that because it has become common among some Catholics to claim that the Immaculate Conception was not fitting in the sense Scotus uses, but truly and actually necessary since, according to them, “In order to be a worthy vessel for the all-holy God, she had to be utterly holy.”
The dicey words in such an argument are “had to.” It’s one thing to say Mary “had to” be holy, if you mean that God’s gracious and unmerited mercy turns out to work in certain ways and not others. But it’s another thing entirely to suggest that God “must” arrange the universe to work in a certain way. When Catholics fail to keep this distinction in mind, they unintentionally end up suggesting that God was under some preexisting, independent obligation to grant Mary the grace of Immaculate Conception. One typical form of this problematic argument runs:
If God is Holiness Itself, how could He dwell in an unholy vessel? How could the One Who demands holiness from His people (Lev. 19:2) and particularly from the priests who minister before him (Ex. 28:6) [sic] dwell for nine months in an unholy woman!
One can be forgiven for thinking that such an apologetic for the Immaculate Conception pictures a sort of matter / anti-matter explosion should a Holy God come into contact with a sinner. The notion that creeps in is that the Incarnation would have been impossible for God without the Immaculate Conception and that God was therefore obliged by the circumstances in which he found himself to preserve Mary from sin.
Rather than approach the Immaculate Conception in this way I think it’s much wiser to approach it as though God is an Artist or, better still, a Father. The only obligations God is bound by are those he places on himself. So, for instance, God “has to” speak the truth, not because he is under some exterior constraint, but because truth is his nature. In the same way, steel “has to” be strong because that’s what steel is. Likewise, God “must,” in the end, “render to every man according to his works: to those who by patience in well-doing seek for glory and honor and immortality, he will give eternal life; but for those who are factious and do not obey the truth, but obey wickedness, there will be wrath and fury” (Rom. 2:6–8). Again, this is not something he is obliged to do by some law imposed on him, still less because he owes us anything. Rather, it’s the fitting reward justice himself gives in accord with own his nature.
Very well then, men like Duns Scotus asked, “Would the God of justice and mercy grant the first Eve, who he foreknew would betray him, a greater glory in her creation than he would give the second Eve, who he foreknew would be his handmaid forever?” The Immaculate Conception is not a necessity in the sense that the Incarnation would be impossible for God without it. Nor is it something God “owes” Mary any more than he “owes” us salvation. It’s a gratuitous gift, fittingly given to adorn the still more gratuitous gift of the Incarnation. Precisely the nature of the “fit” is that the second Eve would not only receive the grace of sinlessness in her conception, but she would preserve that sinlessness throughout her life. And, like all God’s gifts, it is given to the chosen for the sake of the unchosen—as we shall see more clearly later.
As to how God kept her from sin, Scotus’ contribution to the argument (which, after much mulling over, was eventually received by the whole Church) was to solve the objection that Mary was a daughter of Adam (and therefore afflicted by original sin) before she became an adopted child of God by showing that:
in the order of nature, Mary was a child of Adam before she was justified; but in the order of time, her sanctification coincided with the creation of her soul. (John Hardon, S.J., The Catholic Catechism (Garden City, N.Y.: Doubleday, 1975), 153)
In other words, in the order of nature Mary was headed straight for the quicksand. But in the order of time, God pulled her out of the quicksand’s way, granting her the grace Christ won by his Passion and Resurrection, in anticipation of his sacrifice and not apart from it. And this happened in the first moment of her conception, neither before she came into existence nor at some time after. This argument, which was contested bitterly in some quarters, eventually carried the day and found official theological favor in the popes’ judgments. In 1483, Pope Sixtus IV addressed the controversy over the Immaculate Conception, and gave Duns Scotus’ conclusion in favor of the doctrine papal approval. This approval, it should be noted, did not mean “Everybody but Scotus is wrong.” It simply meant that, in addition to the other theories of how Mary was preserved from sin floating around in the Catholic world, Scotus’ was admitted to the discussion as a legitimate contender.
After this, there wasn’t much of a quarrel in the Church. Most people happily celebrated the Feast of the Immaculate Conception (promulgated in 1476) and the controversy died down (although there were holdouts among some Dominicans, who stuck with Thomas’ theology on Mary’s holiness right up until 1854). But for the average Catholic it was a settled matter that the Church had arrived at a clearer understanding of Scripture by seeing just how full of charis Mary really was when the mysterious angelic greeting “Kaire, Kecharitomene!” gave her a title as pregnant with meaning as her womb (Luke 1:28). Indeed, even early Reformers like Martin Luther had no problem with the doctrine:
It is a sweet and pious belief that the infusion of Mary’s soul was effected without original sin; so that in the very infusion of her soul she was also purified from original sin and adorned with God’s gifts, receiving a pure soul infused by God; thus from the first moment she began to live she was free from all sin. (Martin Luther, “Sermon on the Day of the Conception of the Mother of God,” 1527)