... The third step (beyond the gross and subtle bodies) is the causal body of ignorance or "not-knowing". It is only a state of pure forgetfulness, of the quality of darkness, where there is no thought of well-being nor of the gross and subtle bodies!
The state in which there is no knowledge of anything is the causal body. It is like sleep, but it is not sleep. It is very important to understand this state. Those who enunciate the principle of zero—where there is nothing, only a void — came to this state and turned back, as they say there is nothing ahead. This point is the state of the "unknowable", from the point of view of Western philosophy. This state being bereft of all thoughts, fancies and doubts is taken as transcendental awareness [samadhi] in the form of Self-absorption [nirvikalpa Brahman], and as soon as this void is reached, one is apt to get false satisfaction by saying, "Today I saw Brahman."
When one modification of the mind is stabilised, and another fresh one has not yet risen, the interval or pause between these two—the intervening pause period before sleep sets in and the waking state disappears—is a state of pure forgetfulness. This state of forgetfulness is described in the scriptures as the "borderline of the Self" or the "sheath of bliss" [anandamaya kosha]. 
All the chaos, struggle, infinite number of waves of thought have ceased in this causal body, and therefore there is peace in this third body in comparison with the other two bodies. It is true that the aspirant experiences joy here, but this is neither ultimate peace nor real bliss. One must remember this well. The natural state of all the gods, demons and every human being is in this state, which is the causal body in the form of forgetfulness.
The chief indication of this body is to forget everything. Unless one forgets, one cannot have deep sleep. To say, "I was asleep, but I remembered something", is to say "I never slept." Having deep sleep therefore means not remembering a single thing. In the same way, to sleep while being in the waking state means one enters the causal body, which is the natural state of all human beings. Not knowing anything means you have entered this state.
Even big scholars do not understand the true nature of a human being, let alone the true nature of Shiva. In order to explain that state of human forgetfulness, the way of studying this interval or pause is shown. If anything is difficult, it is to completely stabilise in this state of forgetfulness and to know it thoroughly. With great effort, an aspirant should try to achieve this. They [the scriptures] have particularly laid stress upon this.
The fact is that during the pause between two states, there is nothing but pure consciousness. The state of muni [the silent man] is such that he does not allow a single word to rise, or even if it does rise, he does not allow its meaning to rise. He just lets it slip by. When the word rises and is allowed to impress its meaning on the mind, the world is born. Rejecting the word by not allowing it to carry any meaning to the mind is the eradication of the world. When the word does not energise the mind, then whatever is left is the pure energy of consciousness. To experience this state continuously is what is called the "state of still silence".
The aspirant who is about to put his foot on the third step after climbing the first and second, although he is told that this is the state of pure consciousness, still gets the impression that this state is pure void. By taking the void to be Final Reality, he is unable to witness the void. However, if he goes to the fourth step from the third, and he looks back at the third step, he will not be able to see anything at all, and he will wonder, "How is it that my Guru instructed me to put my foot on a step which does not exist at all!?" The reason is that once pure consciousness is known, there can be no trace of what is called "ignorance". One does not understand what the state of forgetfulness is, and there does not arise any modification in the aspirant's mind except that of pure consciousness.
Consciousness or knowledge presents itself to the aspirant in two ways—the first is when there is an object in consciousness; then it becomes "objective knowledge" and he will experience it as objective knowledge. The second is when there is no object and this will be experienced as pure consciousness. When there is an object, it will be objective knowledge and when there is no object, it is simply pure knowledge, or consciousness.
Except for these two, there arises no other modification in the aspirant's mind. The word "ignorance" is meaningless from the point of view of the aspirant. It is not possible for forgetfulness to exist in this case. Whatever is, will be either knowledge or consciousness. It may be objective or it may be non-objective, but it is all still pure consciousness.
Putting before him the state of the causal body and telling him it is just ignorance, a void, a state of forgetfulness where nothing can exist, helps the aspirant to realise that it is all just pure consciousness.
In order to help a student understand that a tiny dot has no width nor length, the school teacher draws a large dot of great length and breadth on the blackboard. That is how it is here too. If it is not done in this manner, the next step cannot be explained, so who can help it? The aspirant should therefore keep full faith in the Satguru without further argument, taking for granted that there is a state of forgetfulness, and should go on practising it to learn to forget each and everything. He will understand that the causal body is the cause of the previous two bodies. [the gross and subtle bodies]
There is a side curtain on a theatre stage called the "wing" from which actors emerge and into which they again disappear. The natural state of a human being is like this wing on the stage—the state of forgetfulness. From behind the curtain emerge all memories, and they disappear again behind the same curtain.
When we say we have forgotten a thing before remembering it, it means that the thing was abiding in that state of forgetfulness, and it proves that it emerged from that state alone. As opposed to this, when we say that we forgot a certain thing, then it means that the thing that was in the memory has disappeared behind the curtain of forgetfulness. A memory before it is forgotten returns to forgetfulness after it is remembered.
The rising and setting of all ideas are in the womb of the one "forgetfulness" and therefore this state is the common ground for all human beings. By reason of forgetfulness, each human being says he is ignorant and struggles to get at least some kind of knowledge. During this struggle, a majority of those unfortunate ones gain worldly knowledge and completely miss out on gaining true knowledge of their own nature.
That is why, while introducing the causal body described above, the Satguru tells the disciple, "Dear one, you are not the gross physical body and you are not the subtle body, so you better identify yourself with the causal body." The aspirant must attain this state of forgetfulness, and he will come to realise that, "I am definitely not the gross body and not even the subtle body, therefore all the dreams and doubts that arise from both these bodies, do not abide in me. I am complete forgetfulness, bereft of all ideas. The birth and death of the body, the misery, temptations, pain, pleasure, hunger and thirst—none of these can ever touch me. Honour and dishonour exist only in the mind, and a fair or dark complexion belongs only to the body—I am totally detached from these qualities associated with the gross and subtle bodies. Nothing can attach itself to me. I am mere forgetfulness."
Revising this lesson again and again and thus making it firmly established in the heart, the state of forgetfulness without any idea or attachment, thus becomes one's own nature. When this kind of mental practice is firmly established, then the aspirant definitely rises to the third step and becomes steady. Only then can it be said that he has now become worthy of putting his foot on the next and final step of the Supra-causal body.
Before going to the next step, it is necessary to mention the fact that the causal body, although like sleep, is a state distinct from sleep. Furthermore, it is explained that in deep sleep all the senses are in complete repose, therefore no objects exist there. In such a state, each being enjoys the bliss which radiates from his own true nature, but he does not still know who he really is. On waking up from deep sleep, each being describes his own experience in the following manner—"I slept happily and I did not know anything." In this way, he conveys the bliss of his own nature as well as his own ignorance about it. He unknowingly conveys his knowingness of his own ignorance, and thus proves his knowingness, but he does not know his own Self. An heir to a treasure of buried gold coins—in the absence of the knowledge of such treasure—goes about his day begging to make his livelihood. For him, that treasure is as good as not being there at all.
Thus, each human being, going back and coming out of his own nature, dives deep within it and experiences profound bliss, but his deep ignorance about his own Self abides there permanently. It is for this reason that deep sleep cannot be the means of attaining knowledge of the Self, one's own true nature. In deep sleep, the aspirant has no scope at all to study the state, but this is not the case in the matter of forgetfulness. To study forgetfulness means to enjoy the deep sleep state while being fully awake. How to enjoy this wakeful deep sleep is taught by the Satguru.
How does a fish go to sleep while living in water? This you will only understand when you take birth in that species. How can the sleep of a fish not get disturbed by the water entering it's eyes? This secret cannot be known unless one is born as a fish. Thus, how can one enjoy deep sleep while remaining fully awake? One will understand this only by becoming a true son of the Satguru.
Fogetfulness is nothing but deep sleep, yet what is described above is the silence within, which is created knowingly during the stage of wakefulness. It is not deep sleep which comes knowingly, because in deep sleep nothing is known. But in forgetfulness, which is knowingly brought about, the nature of the Self is known. This is the difference between deep sleep and samadhi.
Though it is known that forgetfulness is nothing other than forgetfulness, and nothing is known in that state, the fact is that after everything is forgotten, some knowledge still remains. This can be understood only through the study of forgetfulness. This state is absolutely true. Deep sleep and forgetfulness are both the results of tamoguna, a form of ignorance that lulls the spiritual being away from his true nature.
For example, if an analysis of a piece of coal and a diamond is made, it is found that there is nothing but carbon in both—which means that both are only two forms of carbon. But even if it is true, it is not necessary to say that there is a vast difference in their respective value. When the ingredient of carbon is the same in both, how is it that the diamond shines whereas the coal is black and lustreless? The reason is that the proportion of carbon is different in both. Likewise, deep sleep and forgetfulness share different proportions of ignorance and that is why in deep sleep the immense density of ignorance is felt, whereas, in forgetfulness the rarity of ignorance is realised.
As the depth of sleep decreases, the onset of wakefulness rises. The man who has woken up from deep sleep is first slightly under the fuzzy influence of sleep, and then he awakens slowly. This state is the result of the decrease in the depth of sleep until the stark state of full awakeness emerges. Deep sleep is like a pitch black curtain covering the lamp of Self, and the causal body, which is the state of forgetfulness under study, is like a thin transparent velvet curtain. This means that in both these states the enjoyment of bliss is the same. Yet from the point of view of achieving the knowledge of one's own Self, deep sleep is useless. It is like having sexual intercourse with a barren woman while hoping for a child. The study of the anandamaya kosha [sheath made of bliss]  in the form of the state of forgetfulness affords joy, and is a precursor of reaching the goal of knowing one's own Self.
After having said all this, we will now observe the Supra-causal body which is endowed with the knowledge that comes after the study of forgetfulness. Let us digress a little here. ... etc. etc. ...