The main lesson of The Upanishads, a book I just read for the first time, is that the body must be stilled and the mind quieted in order for the ascent to Brahman, or ultimate reality, to be possible.
For someone who hasn’t had any mystical experiences or who hasn’t meditated much, The Upanishads (or The Daodejing or, for that matter, any mystical work) will be intellectually comprehensible and yet will really lack ‘a point.’ It will just be another modern book and therefore will be, once read, assimilated into one’s storehouse of knowledge.
If so, this is a genuine pity, for The Upanishads is an inspired book addressing itself to mystical seekers. As such, it may not be ‘readable’ by, or ‘legible’ to, those who’ve not already set foot onto a path.
It may be asked, “Why is it necessary to ‘renounce’ the body and the mind?” Spiritual teachers, of course, vary on whether renunciation is necessary, but I don’t read The Upanishads as advocating for a renunciation of the body-mind. Rather, I take it that one needs to learn (a) that there’s a reality that is greater than that which available in perceptions of the so-called external or objective world, (b) that there’s a reality that is greater than that which is experienced by the body (i.e., feelings and sensations), and (c) that there’s also a reality that is greater than the mind’s deliverances (i.e., thoughts, images, memories, anticipations, and so on). Consequently, it is not asceticism, pure and simple, that one is learning herein; instead, it’s a genuine inquisitiveness into The More than body-mind. And so, when the sense doors are closed, when the body is so quiet as to be unmoving, when the thoughts and feelings subside, and therefore when one is established in (e.g.) the I Am state, it becomes immediately clear to one that there is a–this–greater abiding reality.
Of course, The Upanishads is urging us not just to come to see directly the I Am state but also to go beyond this state in union with Brahman. Hence, the whole book, when rightly understood by the heart, is nothing more than a pointer or, rather, a series of pointers at the ultimate. From the ultimate to the ultimate.
The opening 5-10 minutes of this satsang with teacher Francis Lucille makes the point above marvelously well. When he speaks of the transfer of energy or desire from the the world (more clearly: from body, mind, and world) to Presence, he is echoing the main lesson of The Upanishads. He calls this “conversion” (or “initiation”) and that term seems perfect here.