Tree from the Garden of Earthly Delights, left panel
The question of the soul as a tree may appear to be about the tree, or sunlight, but the most interesting part of the relationship, for me, anyway, is that of the tree to earth.
The classic Biblical parable refers to seed and the various kinds of ground it falls in. This relates to the quality of the earth that things grow in; and, by analogy, the quality of our Being-of our humility, the inner earth into which the divine seed of consciousness falls.
When Gurdjieff said that everything is material- and, by the way, that all pleasure is "shit"- he was ultimately referring to this need for a good inner soil, which is, to be exact, a humility. One can't really follow thoughts of his without understanding the wholeness they refer to—and Gurdjieff's comments contain many subtle and wide-ranging references to this wholeness which do not fare well when taken partially, or out of context.
The recognition of one's own nothingness, for one, turns equally on this point; and we can now begin to entertain the idea that a man or woman needs to lower themselves to a position where God becomes visible, rather than climb upwards. Although counterintuitive, it's a point I think Meister Eckhart would heartily agree on; and it explains much of what Gurdjieff said about a new kind of connection to the lower being absolutely necessary if the receiving of higher influences was to become possible.
This "lowering" involves a submission to inner gravity: the ever-increasing sensation of one's inner earth. It inevitably involves an increasing organic contact with one's mortality; and that again is something that cannot be explained, but only experienced. Once one begins, in the midst of good health and without the least depression, to understand and even look forward to one's death: then one has been truly touched by this lowering.
For any of this to take place, one has first to be willing; and that will is directly born of this organic lowering of the soul. Insofar as I bend; thus far do I sense the earth beneath the feet of my soul, the place the roots can grow into.
This sensation of one's inner roots isn't one of comfort. It is, rather, a point of inner work from which there is no escape; a confrontation with one's nature in which the demand cannot be denied. There's a joy here; but it is not ever the one I expect. Eckhart's proposition of the eternal fecundity of divinity finds its home here within me as a living thing.
That is a mystery not to discuss, but to live directly into.