The natural question to ask, once we have heard the story of how the doctrine of the Immaculate Conception developed, is, “If the controversy settled down in the fifteenth century, why did the Church formally define the Immaculate Conception as dogma four hundred years later, in the nineteenth century?”

Here things get interesting and paradoxical. As we have seen, usually the Church defines a doctrine because it is under attack in some way. So, for instance, as we saw with the Theotokos, it was a “grass roots” acclamation that Nestorius tried to stamp out, so the Church defended it by declaring it an official title for Mary. However, the interesting thing is that, in the case of the Immaculate Conception, the Church was primarily motivated by love for Mary, not by warfare with heresy.

So, as Pope Pius IX puts it:

Mindful, indeed, of all these things and considering them most attentively with particular joy in our heart, as soon as we, by the inscrutable design of Providence, had been raised to the sublime Chair of St. Peter—in spite of our unworthiness—and had begun to govern the universal Church, nothing have we had more at heart —a heart which from our tenderest years has overflowed with devoted veneration and love for the most Blessed Virgin—than to show forth her prerogatives in resplendent light.( Pope Pius IX, Ineffabilis Deus)

The reason given by Pius IX for defining the doctrine is deeply Christian: love. The Holy See had been petitioned on the Immaculate Conception for centuries because the vast majority of Catholics already believed it and wanted to see the Church define the doctrine as a sort of love letter toMary. So Pius set up a special congregation to study the matter as well as sending a letter to all the bishops in the world asking them to pray and give him their view of whether he should define the dogma. The response was overwhelming:

We were certainly filled with the greatest consolation when the replies of our venerable brethren came to us. For, replying to us with a most enthusiastic joy, exultation and zeal, they not only again confirmed their own singular piety toward the Immaculate Conception of the most Blessed Virgin, and that of the secular and religious clergy and of the faithful, but with one voice they even entreated us to define our supreme judgment and authority the Immaculate Conception of the Virgin. In the meantime we were indeed filled with no less joy when, after a diligent examination, our venerable brethren, the cardinals of the special congregation and the theologians chosen by us as counselors (whom we mentioned above), asked with the same enthusiasm and fervor for the definition of the Immaculate Conception of the Mother of God. Consequently, following the examples of our predecessors, and desiring to proceed in the traditional manner, we announced and held a consistory, in which we addressed our brethren, the cardinals of the Holy Roman Church. It was the greatest spiritual joy for us when we heard them ask us to promulgate the dogmatic definition of the Immaculate Conception of the Virgin Mother of God.( Ineffabilis Deus)

In short, the basic reason given by Pius IX for the definition of the doctrine was that “the opportune time had come”( Ineffabilis Deus) for this doctrinal love letter to Mary. It was not a response to a crisis nor born out of the necessity of fighting falsehood that threatened the peace of the Church. And yet, in the “inscrutable design of Providence” the dogma of the Immaculate Conception did paradoxically end up serving as an antidote to a great many poisonous ideas that were, in the very hour of its promulgation, beginning to take root all over the world.  Of which more next time.