Saivism is called Trika because it distinguishes three levels of reality: Siva, the Energy, and the individual. These planes correspond to the three levels of experience, upon each of which one energy predominates: the pure knowing Subject, complete in its act of will; knowledge, where cognitive energy reigns; and finally, the level of the object of knowledge wherein activity is exercised.
The appearance of these three divine energies in rapid succession corresponds to the three moments of the universe's differentiated manifestation, and covers the whole field of human experience: "No appearance is not established in the triple conscious energy being expressed through: I want, I know, I do" writes Abhinavagupta. (H.A., p. 13)
But the first two moments are so subtle that they escape the notice of ordinary man, who is ignorant of this process because he lives solely on the level of objectivity and duality. The mystic, in contrast, returns to the initial moment, to that consciousness inherent in the original disturbance, divine excitation. And he tries to keep himself there by remaining deeply aware of his own essence.
Trika texts often compare this divine essence to an ocean: "Homage to the ocean of Saivite consciousness, Essence of the conscious Subject!" says one verse (M.M., p. 106). And in describing how Siva, joyfully united with the Energy in the first moment of ardent expectancy, turns to the universe-about-to-be-born, Somananda offers this analogy: "When a violent agitation suddenly appears in quiet waters, one may notice an imperceptible tremor just as one casts a glance in that direction. This tremor is the excitation which emerges from anticipation." (S.D.I., 13-14)
Further development of this analogy may clarify the three successive moments of manifestation upon which Trika is founded. Sometimes, a luminous stretch of profound quiet will suddenly tremble so that the water vibrates. If the sun is full and strong, the water will seem to break up into countless pieces infinitely reflecting the light (sphurata). This dazzling scintillation seems to renew itself perpetually.
In this same way, the will (or initial desire) is sketched out in the ethereal void of pure Consciousness. It emerges, but is not distinguished from Consciousness, from which it still flows. Consciousness exists in conjunction with light; and all is indivisible in Consciousness as is water and light upon the surface of a vibrant ocean. This too is like an initial glance which captures the universe in a complete, sovereign awareness, prior to cognitive knowledge and known objects. In this first moment, the universe is still not separate from the knowing subject and resides in deep inwardness. This is the plane of the undifferentiated Self, the place of the divine path.
Then the sea's surface undulates, swells and grows hollow; a wave is formed, curling and ebbing. But it is still one with the ocean because it is perceived as a single movement despite its many undulations.
A similar process occurs in the second moment. Consciousness becomes troubled, stimulated by the impulse of desire. Seeking to know, it loses the undifferentiated fullness of the Self and assumes distinctive characteristics. Cognitive energy becomes dualisitic thought, differentiating between subject and object. But it is to thought itself, to consciousness itself, that the form of the object appears. And as with the wave and the ocean, subject and object still possess a single substratum. The Universe is manifest, but internally manifest, in the one thought only, like an impression of pleasure or pain. This is the second moment, the level of knowledge, the plane of the path of the energy.
There comes a time when a tempest stirs up the sea. Enormous and violent waves break one by one, fringed with spray, towering and crashing down, seeming to contain in themselves the entire force of the ocean, from which they ultimately part to subside and die upon the shore.
This constitutes the third moment, when man perceives the universe to be outside of himself. He feels isolated, tossed about on the crest of the waves or dashed by their rolling force; helpless, he is lost in the multiplicity and violence of the waves which hide from him the unity of the ocean and the calm of its depths. At this level subjects and objects are clearly distinguished. The world appears externalized, differentiated, the object being far removed from the subject and from knowledge. This is the level of the known subject, the plane of the path of activity.
Despite the various characteristics of its surface, one must remember that it is always the ocean which we contemplate; beneath the multiple forms of Consciousness, the Essence remains. To rediscover this Essence, the individual who is isolated from original Consciousness must recognize first his identity with the wave, then with the single movement of the ocean that sustains both its swelling and its subsiding – that is, with the energy – and finally, with the limitless sea, undifferentiated Consciousness.
If the three divine energies correspond to successive moments of the universe's manifestation, they also form the three main paths when the universe (or consciousness) returns to non-differentiation. These paths serve as the means of return to original Consciousness, each using as springboard its characteristic energy.
Regarding the highest of the energies, that of Consciousness, one cannot truly speak of a path. This involves pure anupaya. the non-path. If the energy expresses itself as joy, what access "without a [particular] way of being" comes down to is a simple repose in joy. If the will surfaces, the eminent path of Siva presents itself, when the energy of knowledge dominates, the path is said to be that of the energy. And if activity is clearly manifest, it is the path of the individual. 
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In the direction of the return, the energies blend together in the divine Essence. When the three paths are dissolved in joy, this joy is perfected and the original freedom is definitively recovered.
Stanzas of the Tantraloka: The Triple Path
"While to certain conscious subjects the Omnipresent reveals his own Essence in its fullness, to others he reveals it gradually." (I., 140)
"The revelation of his single, omnipresent Essence is supreme Knowledge for the individual. Other knowledge, inferior in nature, offers numerous appearances. It may unfold by the direct path (the divine path), or by indirect paths which proceed from it and become differentiated in a variety of ways." (141)
Divine Path or Path of the Will
That which occurs as an immediate flash, fully revealing the field of pure universal awareness of the Self, is known as the divine path. It appears at the brink of knowledge in the reality of complete union, and is in no way characterized by differentiating thought."
"It is divine nature that is revealed, with intensity and complete clarity. It appears to a few extraordinary beings, without their having to pursue a goal, for their eyes are wide open." (The commentary states that this path is characterized by the uninterrupted expansion of the energy of the will.) (146-147)
Path of Energy or Knowledge
"If one attains universal, undifferentiated awareness of the Self through sustained intellectual pursuit, this is known as the cognitive path. It is achieved by repetition and prompts a certainty based upon such purified thoughts as 'this universe is the Self.'"
Path Of the Individual or of Activity
"In contrast is the path of activity. It is considered to be effectiveness which operates according to the requirements of objective reality, and which corresponds to the functioning of this knowledge."
"But in terms of liberation, the differences between these paths does not make one preferable to another, the goal of all being one – Siva himself." (149)
"The distinction between path and goal is based on an error which arises from gross knowledge and which is inherent in the energy of activity. In creating diversity, it is the sole cause of both bondage and deliverance." (145)