Rudolf Steiner expands upon the esoteric meaning of chapter 15 of the Bhagavad Gita:
“If we observe clearly we come to a place in the Gita which, if we have already been amazed at the great and mighty contents of the Gita, we must infinitely extend our admiration. We come to a passage which, to the man of the present day, must certainly appear incomprehensible; wherein Krishna reveals to Arjuna the nature of the Banyan/Ashvatha-tree, of the Fig-tree, by telling him that in this tree the roots grow upwards and the branches downwards; where Krishna further says that the single leaves of this tree are the leaves of the Veda book, which, put together, yield the Veda knowledge. That is a singular passage in the Gita. What does it signify, this pointing to the great tree of Life, whose roots have an upward direction, and the branches a downward direction, and whose leaves give the contents of the Veda? We must just transport ourselves back into the old knowledge, and try and understand how it worked. The man of today only has, so to say, his present knowledge, communicated to him through his physical organs. The old knowledge was acquired as we have just described, in the body which was still etheric (Sunday body), not that the whole man was etheric, but knowledge was acquired through the part of the etheric body which was within the physical body. Through this organism, through the organisation of the etheric body, the old knowledge was acquired. Just imagine vividly that you, when in the etheric body, could perceive by means of the serpent. There was something then present in the world, which to the man of the present day is no longer there. Certainly the man of today can realise much of what surrounds him when he puts himself into relation with nature; but just think of him when he is observing the world: there is one thing he does not perceive, and that is his brain. No man can see his own brain when he is observing; neither can any man see his own spine. This impossibility ceases as soon as one observes with the etheric body. A new object then appears which one does not otherwise see — one perceives one’s own nervous system. Certainly it does not appear as the present-day anatomist sees it. It does not appear as it does to such a man, it appears in such a way that one feels: “Yes! There thou art, in thy etheric nature.” One then looks upwards and sees how the nerves, which go through all the organs, are collected together up there in the brain. That produces the feeling: “That is a tree of which the roots go upwards, and the branches stretch down into all the members.” That in reality is not felt as being of the same small size as we are inside our skin: it is felt as being a mighty cosmic tree. The roots stretch far out into the distances of space and the branches extend downwards. One feels oneself to be a serpent, and one sees one’s nervous system objectified, one feels that it is like a tree which sends its roots far out into the distance of space and the branches of which go downwards. Remember what I have said in former lectures, that man is, in a sense, an inverted plant. All that you have learnt must be recalled and put together, in order to understand such a thing as this wonderful passage in the Bhagavad Gita. We are then astonished at the old wisdom which must today, by means of new methods, be called forth from the depths of occultism. We then experience what this tree brings to light. We experience in its leaves that which grows upon it; the Veda knowledge, which streams in on us from without.
The wonderful picture of the Gita stands out clearly before us: the tree with its roots going upwards, and its branches going downwards, with its leaves full of knowledge, and man himself as the serpent round the tree. You may perhaps have seen this picture, or have come across the picture of the Tree of Life with the serpent; everything is of significance when one considers these old things. Here we have the tree with the upward growing roots, and the downward-turning branches; one feels that it goes in an opposite direction to the Paradise-tree. That has its deep meaning: for the tree of Paradise is placed at the beginning of the other evolution, that which through the old Hebrew antiquity passes on into Christianity. Thus in this place we are given an indication of the whole nature of that old knowledge, and when Krishna distinctly says to his pupil Arjuna “Renunciation is the power which makes this tree visible to mankind,” we are shown how man returns to that old knowledge when he renounces everything acquired by him in the further course of evolution.”
Bhagavad Gita Chapter 15 The Supreme Self
Sages speak of the immutable ashvatha (banyan) tree, with its roots above and its branches below. On this tree grow the Vedas (scriptures); seeing their source, one knows their essence.
Nourished by the gunas, the limbs of this tree spread above and below. Sense objects grow on the limbs as buds; the roots hanging down bind us to action in this world.
The true form of this tree – its essence, beginning, and end – is not perceived on this earth. Cut down this strong-rooted tree with the sharp ax of detachment; then find the path which does not come back again. Seek That, the First Cause, from which the universe came long ago.
Not deluded by pride, free from selfish attachment and selfish desire, beyond the duality of pleasure and pain, ever aware of the Self, the wise go forward to that eternal goal. Neither the sun nor the moon nor fire can add to that light. This is my supreme abode, and those who enter there do not return to separate existence. An eternal part of me enters into the world, assuming the powers of action and perception and a mind made of prakriti. When the divine Self enters and leaves a body, it takes these along as the wind carries a scent from place to place.
Using the mind, ears, eyes, nose, and the senses of taste and touch, the Self enjoys sense objects. The deluded do not see the Self when it leaves the body or when it dwells within it. They do not see the Self enjoying sense objects or acting through the gunas. But they who have the eye of wisdom see.
Those who strive resolutely on the path of yoga see the Self within. The thoughtless, who strive imperfectly, do not.
– Eknath Easwaran’s English translation