The lower path is for the yogi whose existence is defined by the structure of perceptible things. He lives on the level of duality, although he tries to disengage himself from it. He has not renounced all concern for his personal well-being, and remains subject to desire and its upheavals: attraction and aversion. To escape desire, he aims at the true knowledge of the path of the energy, to which the lower path leads.
As the grace available to him remains weak, he surmounts with difficulty numerous obstacles. He courageously tries to end the impurity of utilitarian action and the illusion of duality for these impurities restrict the conscious light to only that necessary to satisfy the needs of limited activity.
He struggles to free himself from doubts and conflicts, and to calm those tendencies centered on the ego in order to regain and exhibit noble and disinterested activity, and to attain its source – divine energy. To do this, he develops concentration at different levels: the body, the breath, the voice, and the intelligence. He recites sacred formulas, gives himself to sonorous articulation, to breathing exercises, meditations, and various contemplations.
He thus purifies his various activities of their tendencies toward dispersion while remaining vigilant in the course of all his occupations, and in waking, dreaming, and deep sleep. But as this purification does not extend to his superior faculties nor to his unconscious tendencies, his bonds will be broken only after death.
Slowly he succeeds in turning himself from the external and from his preoccupation with things. With rapture, he discovers the internal life and his whole being expands there in peace and happiness; his knowledge becomes pure and his heart burns with vitality.
But he only touches Reality: his experiences, as extraordinary as they may be, are fleeting, fragile, and his devotion to God remains tentative. Though he begins to raise himself above contingencies, he is not truly freed from his individual ego.
The dangers which await him are numerous indeed, coming in the form of attraction: to the pleasures of the world, or to supernatural powers. Because he lacks vigilance and ardor, he falls easily from the Fourth state. He advances imperceptibly to the purified energy, and then to the state of Siva with which he becomes one and the same.
At first, the yogi's purifying progress involves the organs (karana) because he is moving towards total mastery of the mystical life with all its various faculties. The individual, by definition "one who is tied to his organs,"  these same organs must thus lend their support to his liberation.
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Through this practice, all preceived objects are subordinated to knowlege, filled by it, and transformed in it. This knowledge, becoming in turn limpid and transparent, reaches the knowing Subject which perceives everything in the mirror of immaculate Consciousness. 
But in the lower path, when the yogi regains contact with his own conscious essence, then his sense organs, his breath, and his intelligence are purified and can thus assist him in the attainment of the Self. In his Tantraloka (v. 10-19) Abhinavagupta explains how:
If intelligence oriented towards unconscious objectivity continues to discriminate between the forbidden and the permissible, it leads to contemplation when it becomes absorbed in Consciousness. Similarly, the breath (prana) which is naturally unconscious and divided becomes a spiritually rising breath as soon as it imbued with consciousness. The unconscious body, whose activity is impure, expresses itself through purified organs when it is illumined by Consciousness.
So, in sum, the exercises of the lower path serve to do away with the determinism that stifles consciousness on the level of the object and to dissolve the unconsciousness that inhabits the body, the breath, and the intelligence, so that only Consciousness reigns.
Therefore, one endowed with intelligence, breath, and body can transform his differentiated thoughts into perfect Consciousness by turning inward.
The Yoganga or Limbs of Yoga
One might question the value of yoga practices in the eyes of Abhinavagupta and his teachers. Their position is clear, and requires precise distinction between the different levels of realization. "The exercises that lead toward liberation are for people who function under the influence of attraction and repulsion and cannot enter into the divine Essence made of grace. Necessarily limited, they do have recourse to exercises and to a variety of practices."
We will see that in the higher path of the energy, these disciplines, including samadhi, must be rejected because they are incapable of revealing Consciousness. The only exception is the knowledge which arises from discrimination.
As for the yogi whose intelligence is very sharp – in contrast to the great yogi who need take no intermediate steps to enjoy supreme power – he must struggle from one power to another until he reaches their source, the absence of discursive thought. Nevertheless, though all of his means may be devoid of the ultimate power (virya), they are not without a certain strength, just as a eunuch who is without virility (virya), is not entirely bereft of force, like a corpse. (T.A. V. 158)
Hence the different limbs of yoga, from the easy postures to samadhi, in certain tantras assume a meaning different from that expressed in the Yogasutras. [a]
Thus asana is defined in the Yogasutras as "an easy and stable posture, for in it effort is suspended and the experience of unity arises such that the yogi can escape contradictions." (1, 46-48). But in the Netratantra, asana becomes the posture wherein one "becomes established in the junction between the inhalation and the exhalation, in the center of the breath. There, established in perfect vigilance, one experiences cognitive energy." (VIII. 11, 18)
In the Yogasutras (49-53), pranayama, breath control, is a pause between the inhalation and the exhalation. The breath's outward, inward, and suspended movements are regulated as to positioning and frequency, so that the whole movement of the breath becomes long and subtle. The fourth pranayama  refers to the external and internal domains. Ultimately, the veil covering the light of (discriminating knowledge) slowly diminishes and thought becomes capable of concentration.
The Netratantra [b, c] specifies a much higher level: "true breath control in the inner path aims to end gross forms of inhalation and exhalation and, further, through the breath inside the breath, to obtain the supreme vibration that goes even beyond the subtler one. Internalizing the breath during the rising of the energy udana known as kundalini. one reaches a point of being continuously in the Center, incapable of falling from it."
[b. A Kashmiri Saiva text, which takes its name from Siva as Netranatha ('Lord of the Eye').
Such an elevation of the inner breath occurs only in a yogi in samadhi, having attained the level of pure conscious Subject.
Thus pranayama no longer appears to be control of the breath in a perfect quiet that protects against the rumblings of the external world. Rather, it is the power of Life itself, as Mahesvarananda states so well: "Whether the power is active or at rest, if one is to recognize one's own Reality, one must understand breath control to be the dissolution of external events." (43) In the eyes of the yogi, events no longer exist, in the sense that they no longer unfold outside of the Self – they are no more than the play of his own power.
Pratyahara is withdrawal of the energy of the organs. According to the Yogasutras (54-55), sensory functions follow the nature of Consciousness when they are no longer in contact with specific objects. Complete mastery of the senses proceeds from this withdrawal. In the Netratantra, the withdrawal that breaks the bonds connected to becoming does not involve the organs relative to external objects. It has instead to do with inner organs that have become infinitely subtle as a result of properly understood pranayama. The objects of these inner organs are whirlwinds of extraordinary qualities, sounds, and lights, surging up without external cause and perceived only by the heart. To turn from these organs and to penetrate into the supreme resting place by means of one's own heart – this is known as withdrawal, the means by which one breaks the bonds of becoming.
The Higher Limbs of Yoga
Concerning the higher limbs of Yoga, dharana, dhyana, and samadhi – the Yogasutras give the following definitions: "Concentration is the fixing of Consciousness on a single point. Meditation is the unification of thought upon this point. When Consciousness empties itself of its own form and manifests as the thing in itself, this is samadhi, absorption." (III. 1-3)
The Netratantra reverses the order of the two first limbs, beginning by defining dhyana in the sense of meditation: "The supreme Reality cannot be an object of meditation. Awakened beings know that true meditation is beyond qualities of thought; it is meditation (the gathering together of oneself) upon supreme Reality as (pure Subject), and of which one has an immediate experience."
When he discovers the Self in his own heart, the yogi passes on to concentration (dharana): "When the supreme Self is perpetually 'fixed' (dha), such a 'concentration' becomes an obstacle to the bonds of becoming." Through it one forever "retains" supreme Consciousness.
Then follows a samadhi of cosmic proportions: "The Consciousness of sameness in oneself and in others, in the elements and in the entire world, the realization that 'I am Siva, I am without-second,' this is when one recognizes the supreme equalization, that is, samadhi or absorption into absolute Reality."
Concentration or Meditation (buddhidhyana)
The culmination of the path of the individual is a meditation which begins intellectually and ends in mystical contemplation, leading to the quieting of and repose in the heart (cittavisranti).
The Vijnanabhairavatantra [d] defines true meditation: "in truth, meditation is an unshakeable intellect, without appearances or solid foundations. Images of divinities that have bodies, organs, faces, and hands, have nothing to do with true meditation." (146)
And in verse 49 Siva speaks to the Goddess Energy: "Oh Fortunate One, She who, senses annihilated in the heart space and spirit indifferent to all other things, reaches the middle of the tightly closed section of the lotus, She will attain the supreme favor."
For according to another Tantra: [?] "If omnipresent Consciousness fills the entire body, it has the ocean of the heart lotus as its eminent residence."
If one is to penetrate into the heart, the breath must come to rest outside the reach of the senses, between the two movements of inhalation and exhalation. In this repose, which lasts only an instant, these breaths balance then cease, producing the opening of the lotus of the heart." (P.H., p. 217)
Abhinavagupta provides a detailed explanation (T.A., V. 21): one who knows the Reality of the Self sees this consciousness directly in the heart as he moves from the external to the innermost recesses. This process is like removing one by one the petals of a kadali flower, with its two intertwined sections. One then attains the center, the perfumed pollen.
During this meditation one progresses from the gross to the subtle, then to the supreme, the sanctuary of the heart where the Self shines forth.
There the all-penetrating Consciousness reveals itself, for Abhinavagupta states:
"It is in the great sacrificial site called the "heart" that the fire-of the powerful Bhairava [e] burns profusely, as one rubs together two sticks of wood.  One concentrates solely upon the friction that unifies all triplicity – moon, sun, and fire, symbols of the inhaled, exhaled and rising breaths, or of the known object, knowledge, and knowing subject."
[e. Supreme Reality, synonymous to Para Brahman. en.wikipedia.org/wiki/
"The resplendent flame of Bhairava – fire or pure Subject – is endowed with an intense energy that expands at the Center. With its help, one recognises that all the triads of energies perpetually surging forth are fusing in a complete non-differentiation of subject, object, and knowledge." (22-25)
The yogi lives in the Fourth state from the time that duality is no more. From this contemplative state he turns toward the external world and, through his purified faculties, begins to perceive Siva even in his ordinary activitues. He then applies himself to the practice of the wheel of conscious energies:
"To live in the undifferentitated, even when differentiation is taking place, this is the supreme and sudden 'roar' of a yogi." (V. 127)
"When the yogi has immediate experience of the undifferentitated Self, radiating from conscious light, his internal organs of knowledge – thought which rests in its own essence, as well as all the sensory organs which depend upon it – lend him their support for penetrating into the ultimate Self that is revealed in all its splendor. At this moment the objects of the senses and the impressions of pleasure and of pain appear to the yogi in great intensity. Enriched by the rays of his fully expanded organs, he devotes himself to making all that appear clearly but without differentiation. Ohl How worthy of seeking is such a Realityl"
He who meditates without interruption upon the process of creation, maintenance and reabsorption as identical to his own consciousness becomes identified with Bhairava and thus realizes the Self as the light of the Wheel of conscious energies.
Through the Wheel of fire (whose center is the heart), the yogi expands his awareness throughout the objective world. He does this fleetingly as emanation, then in a lasting manner as knowledge, and finally reabsorbs it as the knowing subject. In order for this wheel to reach its total undifferentiated fullness, the yogi must dissolve the remaining permeations of duality. He therefore contemplates his faculties as imbued with divinity, as the wheel slowly calms, finally becoming pacific.
At the beginning, the yogi concentrates on the wheel in order to perceive its whirling throughout his various activities. If he hears a sound, for example, unshakeable as an indivisible central axis, he must penetrate to the heart without losing Self-consciousness. (M.M.i 53)
The Sacrifice of the Objective World
The many efforts of the individual traveling this path lead to the great sacrifice, wherein all the impressions of the knowable world are poured like an oblation into the brazier of the supreme Energy. The ensuing nectar fills the universe with vitality and bliss. Abhinavagupta writes, "without this oblation," the universe is torment." (V. 66)
But to offer this sacrifice, a yogi must renounce his individual being. He must perpetually contemplate as identical to the Lord the divine energy in all its fullness. This is the beatific union of Siva and the Energy that gives rise to the universe in the form of nectar, the same and only nectar that is both within us and outside of us.
For the yogi to penetrate into supreme Reality and become established in the state beyond acceptance and rejection, he must perceive the universe in its non-differentiation and attain the quiet of his own essence. This is possible with the help of the rapture that he experiences within his own consciousness. It is accomplished by abandoning the piteous state that comes from intentional activity – that is, activity tied to objects because of their utility, or to impressions of pleasure etc. (74-76)
The path of the individual leads to that of the energy when, his organs stabilized, the yogi is not even aware of concentrating on the extraordinary wonder that delights him:
"All the sensory agitations disappear once he is united to the great and unforeseen wonder. His completely unified organs are like a wheel whose spokes flow forth and at whose heart is a great abundance. And he remains there. He is unburdened by concerns and perceives things clearly. The Consciousness he attains is such that its sparks are sufficient to reduce to ashes the abode of becoming." (84-85)
He begins to have a glimpse of the universe in its non-differentiation, transformed, as it were, and recognized as the precious marrow of pure Consciousness.
Abhinavagupta states that "these beings experience true rapture extending into their daily activities. They remain in the Self."
When this contemplation consists solely of a practice with its vigilant exercises, it is no more than the path of activity.
With the path of knowledge, however, the operation of the energies is spontaneous. According to one verse, "wherever the yogi goes, all the wheels turn around him like a swarm of bees around the queen bee." (T.A. V. 30)
At its highest level, this contemplation leads to the divine path: "He who dissolves the universe into his own consciousness at every instant and produces it again is forever identified with Bhairava. He is free to produce and dissolve the universe. Consciousness reveals itself to him in all its glory." (V. 36)
The lower path offers the deeply calmed yogi successive stages of extraordinary peace and bliss in equal measure to his discovery of the inner mystical life. He need not leave his quieted heart in order to come into contact with the external world. He can, at will, draw unto himself a world completely vibrant with consciousness, consisting of a series of joyous exchanges that fuse in perfect unity, culminating in the flame that consumes all contingency and all unconsciousness. Thus the incomparable Wheel of perfectly unified multiple energies vibrates at an incredible speed, all the while remaining immutable.
This path also includes a series of experiences that are at once "signs" of the purifying path the yogi follows and phases of the vibration (spanda) he feels in the various centers  of his subtle body. These are: feelings of joy, trembling, a particular type of sleep, and fleeting moments of rapture. All of these are his reactions to Reality touching the centers one by one. And as long as he has still not mastered the centers, he bears these touches of reality with difficulty.