According to the Esoteric Science of Theosophy:

“Life is not the result of the operation of the organs, nor is it gone when the body dissolves. It is a universally pervasive principle. It is the ocean in which the earth floats; it permeates the globe and every being and object on it. It works unceasingly on and around us, pulsating against and through us forever. When we occupy a body we merely use a more specialized instrument than any other for dealing with both Prana and Jiva. Strictly speaking, Prana is breath; and as breath is necessary for continuance of life in the human machine, that is the better word. Jiva means “life,” and also is applied to the living soul, for the life in general is derived from the Supreme Life itself. Jiva is therefore capable of general application, whereas Prana is more particular. . . . whether we are alive or dead, life-energy is still there; in life among our organs sustaining them, in death among the innumerable creatures that arise from our destruction. We can no more do away with this life than we can erase the air in which the bird floats, and like the air it fills all the spaces on the planet, so that nowhere can we lose the benefit of it nor escape its final crushing power. But in working upon the physical body, this life – Prana – needs a vehicle, means, or guide, and this vehicle is the astral body.”

– William Q. Judge, “The Ocean of Theosophy” p. 37-38

The Sanskrit term “Jiva” is sometimes used in Theosophical teachings with various different meanings. In “The Secret Doctrine,” for example, H. P. Blavatsky occasionally uses it as a synonym for the Monad and on other occasions for the Ego, the reincarnating soul, our 5th Principle of Higher Manas. Since the word literally means “life,” it could potentially be applied to anything, since ALL IS LIFE. In the Vedanta philosophy of Hinduism, “Jiva” almost exclusively means the reincarnating soul. As said by Mr Judge, “Prana” is the better word to use when discussing the vital force or life energy within us, since this word has only one main meaning metaphysically. That is, “vital breath” or the “breath of life” within us.

On p. 176 of “The Key to Theosophy,” HPB explains that “Prana,” or “Life,” is, strictly speaking, the radiating force or Energy of Atma – as the Universal Life and the ONE SELF, – ITS lower or rather (in its effects) more physical, because manifesting, aspect. Prana or Life permeates the whole being of the objective Universe; and is called a “principle” only because it is an indispensable factor and the deus ex machina of the living man.”

Theosophy teaches the existence of a subtle, unseen, astral body (Linga Sharira in Sanskrit) which is the blueprint, framework, and mould upon and around which the outer shell of our physical body is built. The physical body is the vehicle for the astral body and the astral body is the vehicle for Prana. This “astral double,” as it is also called, is in effect the energy body since it is the vehicle through which Prana (life energy) flows to the physical body.

We might naturally be inclined to assume that tiredness, exhaustion, fatigue, and sleep are caused by a lack of Prana or by much of our Prana having been used up for the day or by something preventing or blocking the proper flow of Prana through our astral body into our physical.

According to the Ancient Wisdom, however, it is just the opposite. Tiredness, sleep, and so forth, are caused by too much Prana, not by too little Prana. We all vary in our ability to handle and cope with the constant influx of Prana into our physical system during waking life. Some are only able to cope with a relatively small amount and thus need more rest and sleep than others. This is particularly noticeable in the young and the elderly, due to the comparatively weaker states – on the two opposite ends of the spectrum – of the physical organism. What modern science generally calls “life,” “vitality,” or “energy” is in most cases not Prana itself but merely the effects of Prana in the physical workings of our bodily system. Prana itself is something metaphysical.

The following passages, from HPB and her friend and colleague William Judge, describe this in more detail:

“Sleep is a sign that waking life has become too strong for the physical organism, and that the force of the life current must be broken by changing the waking for the sleeping state. Ask a good clairvoyant to describe the aura of a person just refreshed by sleep, and that of another just before going to sleep. The former will be seen bathed in rhythmical vibrations of life currents – golden, blue, and rosy; these are the electrical waves of Life. The latter is, as it were, in a mist of intense golden-orange hue, composed of atoms whirling with an almost incredible spasmodic rapidity, showing that the person begins to be too strongly saturated with Life; the life essence is too strong for his physical organs, and he must seek relief in the shadowy side of that essence, which side is the dream element, or physical sleep, one of the states of consciousness.”

– H. P. Blavatsky, “Transactions of the Blavatsky Lodge” p. 71

“The body . . . is like mother earth in that it is made up of a number of infinitesimal “lives.” . . . One of the mysteries of physical life is hidden among these “lives.” Their action forced forward by the Life energy – called Prana or Jiva – will explain active existence and physical death. They are divided into two classes, one the destroyers, the other the preservers, and these two war upon each other from birth until the destroyers win. In this struggle the Life Energy itself ends the contest because it is life that kills. This may seem heterodox, but in Theosophical philosophy it is held to be the fact. For, it is said, the infant lives because the combination of healthy organs is able to absorb the life all around it in space, and is put to sleep each day by the overpowering strength of the stream of life, since the preservers among the cells of the youthful body are not yet mastered by the other class. These processes of going to sleep and waking again are simply and solely the restoring of the equilibrium in sleep and the action produced by disturbing it when awake. It may be compared with the arc-electric light wherein the brilliant arc of light at the point of resistance is the symbol of the waking active man. So in sleep we are again absorbing and not resisting the Life Energy; when we wake we are throwing it off. But as it exists around us like an ocean in which we swim, our power to throw it off is necessarily limited. Just when we wake we are in equilibrium as to our organs and life; when we fall asleep we are yet more full of life than in the morning; it has exhausted us; it finally kills the body.”

– William Q. Judge, “The Ocean of Theosophy” p. 35-36

“This brings us to an interesting theory offered by Theosophy respecting life itself as exhibited by man, his death and sleep. It relates also to what is generally called “fatigue.” The most usual explanation for the phenomenon of sleep is that the body becomes tired and more or less depleted of its vitality and then seeks repose. This, says Theosophy, is just the opposite of the truth, for, instead of having suffered a loss of vitality, the body, at the conclusion of the day, has more life in it than when it waked. During the waking state the life-waves rush into the body with greater intensity every hour, and, we being unable to resist them any longer than the period usually observed, they overpower us and we fall asleep. While sleeping, the life-waves adjust themselves to the molecules of the body; and when the equilibrium is complete we again wake to continue the contest with life. If this periodical adjustment did not occur, the life current would destroy us. . . . Children, say the Adepts, sleep more than adults, and need earlier repose, because the bodily machine, being young and tender, is easily overcome by life and made to sleep.

“Of course, in so short an article, I cannot elaborate this theory; but, although not probably acceptable now to Science, it will be one day accepted as true. As it is beginning to be thought that electricity is all-pervading, so, perhaps, ere long it will be agreed that life is universal even in what we are used to calling dead matter.”

– William Q. Judge, “Echoes from the Orient” p. 17-18

For further insights into some of the concepts mentioned in this article, please see 12 Things Theosophy Teaches, The Sevenfold Nature of Man, Mysteries of the Astral Body, The “Etheric” Body Does Not Exist, Atman – The Higher Self, Manas – The Mystery of Mind, Understanding Our Seven Principles, Definite Words for Definite Things, Theosophy: The Ancient Wisdom, Pranayama and Raja Yoga, Our Sun and The True Sun, Chakras – The Centres in The Astral Body, Living Consciously, and How to successfully study the Teachings of H.P. Blavatsky.

~ BlavatskyTheosophy.com ~