When Mary has taken root in a soul she produces in it wonders of grace which only she can produce; for she alone is the fruitful virgin who never had and never will have her equal in purity and fruitfulness. Together with the Holy Spirit Mary produced the greatest thing that ever was or ever will be: a God-man. She will consequently produce the marvels which will be seen in the latter times. The formation and the education of the great saints who will come at the end of the world are reserved to her, for only this singular and wondrous virgin can produce in union with the Holy Spirit singular and wondrous things.
When the Holy Spirit, her spouse, finds Mary in a soul, he hastens there and enters fully into it. He gives himself generously to that soul according to the place it has given to his spouse. One of the main reasons why the Holy Spirit does not work striking wonders in souls is that he fails to find in them a sufficiently close union with his faithful and inseparable spouse. I say "inseparable spouse", for from the moment the substantial love of the Father and the Son espoused Mary to form Jesus, the head of the elect, and Jesus in the elect, he has never disowned her, for she has always been faithful and fruitful.
St. Louis de Montfort, Treatise on True Devotion to the Blessed Virgin Mary, #34-35