The principal idea which gives shape to the spirituality of St. Louis Marie de Montfort is his understanding of Jesus Christ as the "Eternal and Incarnate Wisdom of God". He introduces and develops this idea in one of his earliest writings, "The Love of Eternal Wisdom" (LEW), which (it is generally thought) he composed in 1703 or 1704. But the title "Eternal Wisdom" is one which he employs in all his writings and throughout his life.
True to his underlying vision of Christian spirituality, St. Louis Marie begins with an exposition of the invitation to humankind issued by Wisdom in the biblical Book of Wisdom, chapter 6:
Wisdom is better than strength and prudence is better than courage. Listen, therefore, kings, and understand. Learn, you judges of the nations... desire ardently to know my words, love them and you will find instruction in them... Wisdom is resplendent and her beauty never fades. Those who love her will have no trouble in recognising her; and those who seek her will find her... she goes around seeking those worthy of her, graciously shows her ways to them, guides them and provides for them with loving care...
It is an invitation to recognise the love which God has shown mankind, and to respond to that love. God has loved us first, and longs for our love in return - this is the underlying theme of the whole book. But, as St. Louis Marie says:
Can we love someone we do not even know? Can we love deeply someone we know only vaguely? (LEW 8)... To know Jesus Christ incarnate Wisdom, is to know all we need. To presume to know everything and not know him is to know nothing at all. (LEW 11)
Here, St. Louis Marie is referring to the only worthwhile knowledge, the only wisdom which can truly give meaning to our lives. He acknowledges that there are other forms of so-called "wisdom" - the "wisdom of the world", or "natural wisdom" - but believes that these can never lead to real happiness (LEW chapter 7). God's wisdom, revealed to us in Jesus Christ, is alone able to do that. And so he sees Jesus Christ as the personification of that wisdom of God, which is "eternal" (having existed from all eternity) and "incarnate" (manifested in the human flesh of Jesus). And, if we wish to achieve real happiness ("salvation"), we need to "acquire" this wisdom - to come to know Jesus Christ and to love him and commit ourselves to relationship with him.
Much of the body of this book is devoted to a meditation on the love God has shown us in Jesus Christ, and on the "gentleness" of Jesus himself. It is clearly St. Louis Marie's aim to persuade us to make the effort to "acquire" divine Wisdom, by helping us to see how loveable he is. In pursuit of this aim, he includes two chapters on what he calls "the most convincing reason for loving Wisdom" - namely, "the suffering he chose to endure to prove his love for us" (LEW 154). Here he speaks also of the Cross of Christ as "the greatest secret of the King" (LEW 167), through which Eternal Wisdom triumphs. This understanding of the Cross is a major element in the total spirituality of St. Louis Marie, and his meditation here sets the scene for another of his writings, a little work entitled "Letter to the Friends of the Cross".
And so, in the final chapters (15, 16 and 17) of this book, St Louis Marie speaks of the principal means to "acquire" and "preserve" divine Wisdom. They are, he says, four:
This last means (devotion to Mary), he says, is "the greatest means of all, and the most wonderful of all secrets for obtaining and preserving divine Wisdom". Chapter 17 (in which he speaks of this) could be seen as a summary of what he writes in both the "Treatise on True Devotion to the Blessed Virgin" and "The Secret of Mary". He speaks of the necessity of genuine devotion to Mary, describes what it is, and finally introduces "the most perfect and most profitable of all devotions to the Blessed Virgin" which consists in "consecrating ourselves entirely to her and to Jesus through her as their slaves." This is the devotion known variously as "Holy Slavery", "Total Consecration to Jesus through Mary" or simply (but too simplistically) "True Devotion".
From this it is clear that, for St. Louis Marie, devotion to Mary is never an end in itself, but a means to a deeper attachment to Jesus Christ, the Eternal and Incarnate Wisdom of God. He makes this abundantly clear also in the Treatise on True Devotion to the Blessed Virgin (see Montfort's Spirituality and Marian Devotion).
At the end of The Love of Eternal Wisdom, St Louis Marie includes the text of an Act of Consecration to Jesus Christ, Incarnate Wisdom, through the hands of Mary. This is the only place in all of St Louis Marie's writings where an Act of Consecration is found, and we should not fail to notice that it is a consecration to Jesus Christ, not to Mary, but through the hands of Mary. Some theologians today would hold that, because of the nature of consecration, the only valid consecration for a Christian is a consecration to God (which would certainly include, of course, consecration to Jesus Christ). In St Louis Marie's day, the word consecration was used less strictly, but he himself recognises the difficulty, and discusses it in the Treatise on True Devotion to the Blessed Virgin, no. 245, where he discusses whether it is better to speak of "slaves of Mary" or "slaves of Jesus through Mary":
It is better to speak of "slavery of Jesus in Mary" and to call oneself "slave of Jesus" rather than "slave of Mary". We then avoid giving any pretext for criticism. In this way, we name this devotion after its ultimate end which is Jesus, rather than after the way and the means to arrive there, which is Mary. However, we can very well use either term without any scruple, as I myself do. If a man goes from Orléans to Tours, by way of Amboise, he can quite truthfully say that he is going to Amboise and equally truthfully say that he is going to Tours. The only difference is that Amboise is simply a place on the direct road to Tours, and Tours alone is his final destination.
In a similar way, he found no difficulty in speaking of "consecration to Mary", but he always had in mind "consecration to Jesus through Mary".
"Eternal and Incarnate Wisdom" was the favourite title applied by St Louis Marie to Jesus Christ, and his vision of Christ as "divine Wisdom" is found everywhere in his writings, where he not only speaks of Jesus as "Wisdom", but writes of the "wisdom of the cross" (Letter to the Friends of the Cross, no. 45), the necessity of continually praying for "divine Wisdom" (e.g. Letters 15 and especially 16), and so on. The word "wisdom" occurs hundreds of times throughout his writing, particularly of course in The Love of Eternal Wisdom, but also (for example) in 79 verses of his Hymns. "Wisdom" is the foundation-stone of the spirituality which he practised and taught.