Where is the “best” part of the soul that God reserves for his abode? Tricky question. There are two common choices in terminology. Some writers and saints say that God’s deepest home in the soul – and thus the resting place of contemplation when we go out into action – is deepest, where it is most interior, like the centre of a series of concentric rings. Meanwhile, others says that God’s deepest home in the soul – and thus the resting place of contemplation when we go out into action – is at the highest point of the soul, like a window at the top of a dome through which light enters and illuminates all.

There is no opposition between these two images. We’re using an image to describe spiritual things. The deepest part of the soul, the highest point of the soul through which heaven can enter: they are the same. The “topography” of the human soul can be sketched two ways. We can make a series of deepening, tightening, concentric circles. We can make a cone with a highest point. Both show that there’s topography. Both point to a “best” or most ontologically dense point.
Examples of those who tend to prefer the image of “depth” are Augustine, Hildegard, Teresa, Alphonsus, and Elizabeth of the Trinity.
Examples of those who tend to prefer the image of “height” are Jane de Chantal, Thérèse, Marcel Văn, Jacques Maritain, and Charles Journet.
And then some, like John of the Cross and Francis de Sales, seem to flit from images of “depth” to images of “height” however it pleases them.
The reasons for these preferences don’t much matter, as long as – and this is the normal expectation – they are not trying to say anything substantially different. For the most part, they are trying to use words to point to a reality that is, in many ways, beyond our words. Words just point to reality. They help us. They aren’t meant to make problems.
Edith Stein has some passages that point out the complementarity of the images and descriptions of “depth” and “height” to a soul:
The soul is positioned in a realm of the Spirit and of spirit. She, however, possesses her own structure. She is more than a simple form that animates the body, more than the interior of an exterior. Rather, within her there lies an opposition between internal and external. The soul can be said to be at home at her most interior point, at her essence or the deepest ground of the soul. She goes out through the activity of her senses to a domain inferior to her realm…
Her action takes her away from the deepest ground or highest window. This is not bad in itself. Action and contemplation tend towards greater union in Christ; and both are real goods. But as contemplative, loving gaze on Christ and on the Trinity become more actualized, the human person goes in to the innermost depth and up to the uppermost height of the soul:
In her ascent to God, the soul raises herself above herself or is raised above herself. But at the same time, by this more than anything else, she actually attains her innermost centre.
Again:
God is the sustaining ground of everything. Whatever ascends to him descends at the same time, by that very act, into its own centre or resting place.
And again:
The higher she ascends to God, the deeper she descends within herself: the union is consummated in the innermost soul, in the deepest ground of the soul. If all of this seems contradictory, it is to be remembered that these are only different spatial images that – by reciprocally complementing themselves – wish to indicate something [the spiritual] that is totally alien to space and for which natural experience cannot supply any adequate delineation.
Deeper and deeper; higher and higher. The call to love, to contemplation, to suffering things divine, to union with the Will of God calls for depth and height to the soul. We must go deeper and higher.
Or, perhaps, in that phrase from Narnia, “further up and further in.”

