The eighth of September is, of course, the Nativity of the Blessed Virgin Mary. It is also the date on which, in 1907, the encyclical letter Pascendi Dominici Gregis was issued by Pope St Pius X.
Whatever its reception at the time, Pascendi can hardly strike the honest reader as some mere doctrinal antique. In fact, more than a hundred years out, we find ourselves well situated—better situated indeed than those to whom the encyclical was first addressed—to see just how valid the observations of Pascendi are. Which is to say that the effects of the heresy of modernism are to be met with everywhere today.
But everyone with eyes to see knows this. What may be less clear, however, is that one of the remedies for this synthesis of all heresies is a Marian one.
At the moment, only this simple observation is being made: that where Mary is, heresy is not. For this reason did Pius X name her ‘the destroyer of all heresies.' Thus, isn’t it worth pointing out that wherever there is dissent and error amidst Catholic opinion today, robust veneration for the Mother of God is conspicuously absent? The very claim itself is divisive and, therefore, demonstrative: to the devout, it will sound perfectly obvious; to the modernist, it will sound credulous, irrelevant, and even ‘pious’ (a tarnished word in the English language as there ever was one.)
But did the saintly Pius X have precedent for referring to the Virgin Mary in this way—namely, as the destroyer of all heresies? In fact, yes: the Roman Breviary tells us so. We go to the third nocturne of Matins in the Common of Feasts of the Blessed Virgin Mary. The first antiphon reads:
Rejoice, Virgin Mary! You alone have brought to ruin all the heresies throughout the world.
Interesting to note that the sacred liturgy ties together joy and the defeat of theological error. Rightly indeed is our Lady exhorted to rejoice. For joy only flourishes with the truth.
The point is further proved for us: the psalm to which this antiphon is attached is the 95th:
Sing the Lord a new song: sing to the Lord, all the earth . . . For he shall judge world in equity, and the people in his truth. 
Study the entire Psalm: no modernist could ever pray it with a sincere heart, for it is precisely the opposite of his doctrine. For the modernist, in the last analysis, never brings himself to praise; the conclusions of his perfidious doctrines never lead to the glorification of God. They lead to a pretended glorification of man, but never to the profound and simple posture to be met with in Psalm 95.
And here, in the Common of Our Lady, she leads this psalm of rejoicing. After all, what else is her Magnificat than a paraphrase of every psalm that gives jubilant praise to ‘the living God, the true God, the holy God’?
It is for this reason that the Virgin Mary is the remedy and conquerer of all heresies—and therefore fitting to the extreme that Pascendi should be promulgated to the churches on the commemoration of her birthday.
 Cf Pascendi, n 39.
 Ibid, 59: ‘adsit prece atque auxilio Virgo immaculata, cunctarum haeresum interemptrix.’
 Gaude, Maria Virgo: cunctas hæreses sola interemisti in universo mundo.
 Cf 1 Corinthians 13, 6.
 Psalm 95, 1 and 13.
 Cf exorcism of the salt at the Rite of Making Holy Water: ‘Exorcizo te, creatura salis, per Deum + vivum, per Deum + verum, per Deum + sanctum, per Deum, qui . . .’