The universal Church celebrates the feast day of this great saint today. St Louis de Monfort is often called the Totus Tuus (I am all yours) saint because of his great devotion to the Blessed Virgin Mary. His most well known work is the Treatise on True Devotion to the Blessed Virgin Mary. He wrote this work while recuperating from the effects of a poisoning inflicted upon him by the Jansenists. St Louis de Monfort prophesied that this work would be hidden by the devil for quite some time; in fact it wasn't discovered until 200 years after his death!
Thankfully this work is still in print today and while it is not an easy read, it is a beautiful and rich one. It has brought many to the heart of Our Lord through His Mother. Many have made the de Monfort Consecration because of this work.
The late Pope John Paul II was also deeply affected and moved by this particular writing by this saint; "Totus Tuus" was his episcopal motto.
Here is an excerpt from the Introduction of True Devotion. You can read more by following the link with the book's title.
Mary is the supreme masterpiece of Almighty God and he has reserved the knowledge and possession of her for himself. She is the glorious Mother of God the Son who chose to humble and conceal her during her lifetime in order to foster her humility. He called her "Woman" as if she were a stranger, although in his heart he esteemed and loved her above all men and angels. Mary is the sealed fountain and the faithful spouse of the Holy Spirit where only he may enter. She is the sanctuary and resting-place of the Blessed Trinity where God dwells in greater and more divine splendour than anywhere else in the universe, not excluding his dwelling above the cherubim and seraphim. No creature, however pure, may enter there without being specially privileged.
I declare with the saints: Mary is the earthly paradise of Jesus Christ the new Adam, where he became man by the power of the Holy Spirit, in order to accomplish in her wonders beyond our understanding. She is the vast and divine world of God where unutterable marvels and beauties are to be found. She is the magnificence of the Almighty where he hid his only Son, as in his own bosom, and with him everything that is most excellent and precious. What great and hidden things the all-powerful God has done for this wonderful creature, as she herself had to confess in spite of her great humility, "The Almighty has done great things for me." The world does not know these things because it is incapable and unworthy of knowing them.
The saints have said wonderful things of Mary, the holy City of God, and, as they themselves admit, they were never more eloquent and more pleased than when they spoke of her. And yet they maintain that the height of her merits rising up to the throne of the Godhead cannot be perceived; the breadth of her love which is wider than the earth cannot be measured; the greatness of the power which she wields over one who is God cannot be conceived; and the depths of her profound humility and all her virtues and graces cannot be sounded. What incomprehensible height! What indescribable breadth! What immeasurable greatness! What an impenetrable abyss!
Every day, from one end of the earth to the other, in the highest heaven and in the lowest abyss, all things preach, all things proclaim the wondrous Virgin Mary. The nine choirs of angels, men and women of every age, rank and religion, both good and evil, even the very devils themselves are compelled by the force of truth, willingly or unwillingly, to call her blessed.
Let us thank Our Lord for raising up this great saint who through his intercession leads so many to our Blessed Mother who leads us to her Son.