It is figuratively said that Sadāśiva appears with a body. In reality, His body is of the nature of five mantras of Śivaśakti. He is with the head formed of Īśana-mantra; faced form of Tatpuruṣa-mantra; heart formed of Aghora-mantra; secret part formed of Vāmadeva-mantra; all other parts of His body formed of Sadyojāta-mantra.
(...) The incredible lordship of Īśvara is at the state of apex, comparable to the highest part of a body, the head. Through the grace-yielding Śaktis which are five in number and which are manifested by Īśana, the Lord compassionately and swiftly manifests the power of knowing and doing within the souls, brings them out of the hold of aṇava-mala and installs them in a pure realm which is at the highest level, like the head. Therefore, the Lord is said to be with the head constituted of Īśana-mantra.
His face is the mass of effulgent Śakti. Through his face He showers profusely the flashing sparks of guiding words and utterances from the fire of knowledge-scriptures and fills the worlds of all adhvas with such sparks. The word ‘puṁ’ denotes purity. He purifies the souls which are living in the world consisting of moving and non-moving things by removing the heap of ignorance from them. Therefore He is called ‘Puṁsā’. The face is conceived to be of the nature of assumptive power (parigraha-śakti) which is all-pervasive. This assumptive power is known as ‘mahāmāyā’ and since it is the causal source of sound, it is conceived as the face. Since the Lord presents Himself in the mahāmāyā conceived in the form of face, He is said to be with the face constituted of Tatpuruṣa-mantra.
It is revealed that the heart is identical with constant oneness with the absolute Existence characterized by śivatva (power of all-knowing and all-doing). The word ‘aghora’ denotes tranquility. Through the constant oneness with Existence (śivatva), He is always in a state of tranquility. The term ‘ghora’ denotes the limiting factors such as mala, likes and dislikes and others. Since He is beginninglessly free from such ‘ghora’, he is called ‘aghora’. Since His heart is identical with the innate nature of tranquility, He is said to be with the heart constituted of Aghora-mantra.
The term ‘vāma’ associated with the word ‘guhya’ denotes the Kriyā-śakti of the Lord. Vāma means strangely or differently formed and guhya means ‘not directly seen’. The Lord who shines forth in the entire range of things (viśvarat) accomplishes the creation of variagated range of worlds and tattvas through the thirteen kalās evolved from the Vāmaśakti (Kriyāśakti). The term ‘vāma’ denotes the nature of being contrary. In this universe, the existence of Sadāśiva is inferred through the activities which are contrary and opposed to each other. Through such activities He grants all the fruits to the hosts of souls as desired by them. Therefore, Lord Sadāśiva is said to be with the secret part constituted of Vāmadeva-mantra.
The term ‘mūrti’ denotes the body. The body of the Lord is of the nature of His own mighty power of knowing and doing associated with the authority over creation. Sadyojāta manifests Himself from the transcendental laya tattva for the sake of cosmic play related to the worlds and the worldly beings. Since he effortlessly leaves out the state of laya and assumes another state, such effortless activity is figuratively termed as ‘play’. He assumes the state of being with a body instantaneously at the very moment He wills to create. Therefore, His form is considered to be constituted of Sadyojāta-mantra. In this way, Sadāśiva appears with a form constituted of these five mantras.
(Matāṅgāgama, Vidyāpāda, 4.14-30)
Because in all His undertakings (He acts) for the benefit of souls, the Lord has His own, full body. This body is full with (His) five mantras: Sadyojāta, Vāmadeva, Aghora and Tatpuruṣa. With these mantras, together with Īśāna, (is made up) the body of the Supreme. This Lord, who has Īśāna for His head, Tatpuruṣa for His mouth, Aghora for His heart, Vāmadeva for His genitals and Sadyojāta for His form, is taught to be composed of parts (sakalaḥ).
His being composed of parts (sākalyam) is not ultimately real, as it is with an ordinary soul, but constructed (kalpanīyam). For otherwise He could not be worshipped by all, being devoid of a body. Therefore this body of that pure (Lord) is fashioned out of pure mantras. Therefore this contrivance of a body is adopted for the sake of worship; since worship is a necessary part of enjoined rites, it must be adopted for the sake of attaining their fruits.
... Since that Śiva-principle is sovereignty (aiśvaryam), consisting of powers of knowledge and action extending to all things, therefore since that rests above, in the way that heads do, the mantra Īśāna stands as the head of beings that are endowed with sovereignty that consists in the powers of knowledge and action, and that are sentient because of the power of the supreme (paraśakticetasām), and therefore He is known as the one with Īśa as His head.
Since it cleans away nescience, and since the word mouth expresses revelation - it reveals through its power of Śivahood - therefore He is taught to have Puruṣa for his mouth. Alternatively, He has the mantra Tatpuruṣa on His face and therefore He has Puruṣa for His mouth.
His essential nature, that is His heart, is non-terrible (aghoraḥ) and therefore peaceful, and that is why because of His essential nature the supreme Lord is one whose heart is Aghora. Alternatively, He is held to have Ghora as His heart (ghorahr̥t) through mantras or through aghoras.
That which is lovely (vāmam), the state of liberation, is hidden; since that is so for Him, or because the path to what is vāma is hidden, His private parts are Vāma.
Since He immediately creates bodies for souls, or because His form is immediately present in front of Yogis, He is taught to be Sadyomūrti.
By the use of ritual gestures, diagrams, the mantras that are His limbs (mudrāmaṇḍalamantrāṅgaiḥ), by focusing the mind, concentration and yoga (dhāraṇādhyanayogataḥ) that Supreme, peaceful (śāntaḥ) Lord is worshipped by those who desire the fruits of supernatural powers and of liberation.
It is that same Lord who is worshipped residing in the body made up of His mantras; He is the Supreme Śiva. Therefore Śiva is established in śastras to be at the same time in two forms: Sakala and Niṣkala. He who is the cause of maintenance, creation and destruction (of the universe) and of compassion is the Lord with office in this sakala state, made up of the parts of the mantras that are His limbs. He reveals their office to the others, to the Rudras and such. Figuratively He is known as the Lord with office (adhikārī), the Lord in enjoyment (bhogī) and the Lord in reabsorption (layī).
The beginningless compassion upon bound souls that is established to have been bestowed by Him, because of His being the Lord, is possible through the teaching of the injunctions of His scripture, through the connection between ācāryas and their pupils. Not otherwise can the state that is in Him (viz., Śivahood) be attained.
(Parākhya Tantra, II.84-100)