Madame Guyon lived from 1648 to 1717. She was a Quietist, which means that she believed in complete passivity with respect to God, "even to the point of not wishing to be saved" (41). Pretty extreme stuff, right?
Biblical exegesis was not something women were trained, encouraged, or allowed to do, but she was pretty dedicated and endeavored to write about the entire Bible. She wrote with vigor and clarity, and I think I will just let some of her words speak for themselves.
I picked this excerpt, which groks on the verse from Song that reads "Let him kiss me with the kiss of the mouth," because it relates to the Trinity, a mystery and a metaphor that has been on my mind a lot lately.
"The kiss which the soul desires of its God is essential union, or a real, permanent and lasting possession of its divine object. It is the spiritual marriage. That this may be understood, it is necessary to explain the difference between a union of the powers and essential union. Either of them may be transitory, and for a few moments only, or permanent and lasting.
"The union of the powers is that by which God unites the soul to himself, but very superficially; it is more properly a touch than a union. It is nevertheless united to the Trinity of persons according to the different effects proper to the individual persons.... This union is accomplished in order, in all the powers of the soul, and is sometimes perceived in one or two of them according to the designs of God, and at other times in all three together. This constitutes the application of the soul to the Holy Trinity according to the distinct persons. When the union is in the understanding alone, it is a union of pure intellect and is attributed to the Word as a distinct person. When the union is in the memory, which is effected by an absorption of the soul into God and a profound forgetfulness of the creature, it is attributed to the Father as a distinct person. And when it takes place in the will alone by a loving joy without sight or knowledge of anything distinct, it is a union of love and is attributed to the Holy Spirit as a distinct person. This last is the most perfect of all, because it approaches nearer than any other to essential union, and is generally the road by which the soul arrives at it. All these unions are divine embraces--but they are not the kiss of the mouth" (42).
The kiss of the mouth is something deeper still, something she goes on to describe as a "spiritual marriage [...] where God takes the soul and unites himself to it, no longer by way of the persons of the Trinity, nor by any act or means, but immediately by reducing all into unity and by possessing it in his own unity. Then it is the kiss of his mouth, and real and perfect possession. It is an enjoyment which is neither barren nor unfruitful, since it extends to nothing less than the communication of the Word of God to the soul" (42).
It seems to me that Madame Guyon explores the massive ineffability of God and how she desires to join with Him not for her sake but because it is Right.
Next, we jump into a new chapter of Christian mysticism with asceticism, the practice of denying oneself bodily pleasures, and sometimes even necessities, for some higher good. For the mystics McGinn looks at, asceticism was a way to prepare oneself for union with God. Remember that asceticism should be (according to McGinn's interpretation of mystical thought, belief, and tradition) a means to an end and not an end itself. Purge so that God may fill.