The simple answer is because she is our Mother in grace. We are born to eternal life by baptism. She brings us to that birth and continues to nourish, educate and protect us. She is with us after baptism and continues the graces flowing from baptism.
When we try to do things on our own, without her, we lose that nourishment. Just as a baby in the womb is helpless without the life giving blood of the mother transmitting all it needs to the baby, we receive all we need supernaturally from Mary.
“All the predestinate, in order to be conformed to the image of the Son of God, are in this world hidden in the womb of the most holy Virgin, where they are guarded, nourished, brought up, and made to grow by that good Mother until she has brought them forth to glory after death, which is properly the day of their birth, as the Church calls the earth of the just.”True Devotion to Mary, by St. Louis de Montfort
“From the day the soul is born again in baptism, on to lifetime’s end, perhaps a hundred years later, no single grace will have reached that soul without Mary.”
And all this is not strange. It is fitting, because God uses what is most like us to reach us. Mary is most like us, and more than anyone our Mother in grace.This article is from a condensation of “the Montfort Way” by Servant of God Frank Duff
Finally, Mary is the triumph of God’s humility over the pride of men and bad spirits.
In the weekly meeting we explicitly give our prayers, our actions, our will and our lives to Mary. No other active lay group in the church does that. We are assigned work by the president and report on it in the spirit of obedience. There is no other lay group that does the spiritual works of mercy in Mary’s name in explicit obedience.*
That explicit obedience makes all the difference. There is no other way for a lay person to get rid of spiritual pride unless they give over their obedience to to Mary. Obedience to Mary is more humble than obedience to Jesus, because she is only human.
IT ALL COMES DOWN TO MARY STANDING AT THE FOOT OF THE CROSS
The love of Mary for us is clearest when she stands at the foot of the Cross. She is weeping, but not for herself. She is standing, when all the others ran away. The only way to look at the Cross is through her eyes of faith that God would raise her son again.
The love of Jesus is fully revealed at the Cross. And His last words before it was finished, were to Mary, “Woman, behold your son.” Then He said to John, “Behold your mother.” Ponder that.