Vashisht Vaid in his blog at https://holysageagathiyar.com/uuw/book-i-spiritual-initiate/chapter-1/ spells out the origin and nature of Agathiyar.
The Great Sage Agathiyar being a Radiant Embodiment of the Vital Consciousness of ‘’Adi Ganesha’’ was also blessed to be partaker of the all the ‘Agamic Wisdom’, which apart from him was shared by the ‘Param Adi Shiva’ only with the Cosmic Mother. Sage Agathiyar based upon his attained knowledge and wisdom, which was bestowed upon him by the Grace of the Great Lord ‘Adi Param Shiva’ then composed a great number of Agamic Texts in the ‘Mother Tamil’.
Lord Dakshinamurthi through the dutiful services of Sage Agathiyar thus revived in the ‘Dravid Vrata’ of ‘Bharat Khanda’, the Advanced Ancient knowledge of Siddha’s known as ‘The Wisdom of Celestial Perfections’, which included the wisdom of the most ancient 10 Shivogamas in their Three Fold qualities [Tri Gunas – viz Satvik, Rajsik, & Tamsik] thus creating the 30 treatise of Shivoagamas in Mother Tamil Language.
All Siddha "Wisdom of Perfections [Siddhis]" vitally existing as the ‘Supernatural Energy Frequency Vibrations’ in the Infinite Universe comes out of the wisdom of these Agamic Texts, spoken at the very beginning of all Creations and manifestations, which were vitally manifested Subjectively and Objectively in the Ethereal Nebulae of the Cosmic Egg [Brahmanda] by the desire mind of ‘Param Adi Shiva’, thus vitally formulating the 5 Rays of intellectual activity and their various Innumerable ‘Permutations and Combinations’ which caused all sorts of Cosmic Geometries [Jyotirmaya Antariksha] of innumerable frequencies in the Infinite Universe [Brahmanda].
In each Kalpa, the seven landmasses under seven Manus appear and disappear one after the other. When the third land mass Kumari Kandam appeared, Erai sent Agathiyar, one of the seven Rishis, as its protector. Agathiyar learned the sciences from Lord Murugan at Pothigai. He mastered the five aspects of Erai that are creation, sustenance, destruction, veiling, and blessing, and also achieved all eight siddhis. Hence he stood as a Vignana Kalar.
Pon Govindasamy in his "Vallalaarum Brahma Gnana Sangamum", Bharath Book Bureau, Chennai, explains the different states including Vignana Kalar. Souls were categorized into three divisions namely: Sakalar, Piralayaakalar and Vignanakalar. The souls who were still tied down to the three Malam namely Aanavam, Kanmam, and Maayai, till they reached the state of a Jeevanmukta are called Sakalar. Dropping Maayai, now these Rishis are known as Piralayaakalar. God comes as guru to these Piralayaakalar. These Maha Rishis in turn educate the Sakalar. The Maha Rishis who had defeated Maayai and Kanmam but are restrained by Aanavam are called Vignanakalar. To these Maha Rishis God comes within to teach. Their vibrations are one.
மக்களை சகலர், பிரளயாகலர், விஞ்ஞானகலர் என முப்பெரும் பிரிவுகளாக வகுக்கப் பெற்றுள்ளன.
ஆணவம், கன்மம், மாயை என்ற மும்மலங்களாலும் கட்டுப்பட்ட சீவன் முக்தர்கள் வரையிலுமான ஆன்மாக்கள் சகலர் எனப்படுவர். சகலருக்கு மகரிஷிகளை அதிட்டித்து நின்று உபதேசிப்பான்.
மாயா மலம் நீங்கி ஆணவம், கன்மம் என்ற இருமலங்களுடன் மட்டும் கூடிய ரிஷிகள் பிரளயாகலர் ஆவர். பிரளயாகலருக்கு இறைவனே குருவடிவம் தாங்கி வந்து உபதேசித்தருள்வான்.
மாயையும், கன்மமும் நீங்கி ஆணவ மலத்தால் மட்டும் கட்டுப்பட்ட மகரிஷிகள் விஞ்ஞானகலராவார். விஞ்ஞானகலருக்கு இறைவன் உள் நின்றே உணர்த்துவன். இது இறைவன் உணர்வும் விஞ்ஞானகலர் உணர்வும் ஒன்றித்த நிலையாகும்.
Pon Govindasamy writes that Agathiyar in this current era was Brahma's representative at the "Antaranga Arul Aratsatchi" based at Chidambaram. He is tasked to look into the affairs pertaining to the portion of the Vedas known as Karma Kanda. Agathiyar goes through each individual's account of merits and demerits (karma). To aid him in this task he has Karma Devas known as Chitraguptas. Besides that, he is responsible for culture, kriya, and agamas. He oversees Sanatana Dharma. Through his thoughts, he drives the scientist and researchers to excel in their fields respectively.
Pon Govindasamy reveals to us the Divine's plan. In his "Vallalaarum Brahma Gnana Sangamum", he states that it is the mission of the Divine to save the souls that are riddled, locked, and chained by Aanavam, Kanmam, and Maayai and bring them back to his state of purity.
கட்டுப்பட்ட உயிர்களை தளை நீக்கி (ஆணவம், கன்மம், மாயை), தன்னைப்போல் அகண்டாகார பரிபூரண வஸ்துவாக மாற்றுவதே ஈஸ்வரனின் சங்கல்பம் ஆகும்.
Gordon Matthews explains this concept in his translation of Meykanda Devar’s "Shivagnana Botham" writes,
“By reason of the soul’s virtue in previous births, God, who has been immanent in the soul, making it known, now vouchsafing to take the form of a Guru, initiates the soul in the Saiva mysteries. The primal one himself teaches these souls as a Guru: for in the form of consciousness, he is in union (with him). When because of the soul’s meritorious practices the primal one enlightens the soul as a Guru…”
We are indeed blessed to have come to be acquainted with a Maha Rishi of such a nature and stature. And it all started with his call to come to his path and worship him and the Siddhas besides the whole pantheon of Gods made through his tool of communication then, the Nadi. The Nadi reading did change our lives for good. Taking heed we started his worship. Love for him began to bloom within our hearts. We began to take his words as Gospel. Compassion for others began to bloom as we began serving the unfortunate as he ordained. He came through his Aasi Kaandam to further guide us. He came as both gurus Supramania Swami and Tavayogi and upagurus to teach and show us the methods of ritualistic worship or agamas and Yogic practices. In their absence in physical form, they come within us to guide us.
Just as he asked if Hanumathdasan Aiya wanted him to shed the majesty of the Tamil language that he so carefully nurtured but did speak in the colloquial language of the day henceforth in all his Nadi readings, Agathiyar has come to us bringing himself from his state of God to Guru to Father and now a fellow companion.
Just as the "Voltage/potential difference can be compared to water stored in a tank. The larger the tank, and the greater its height (and thus its potential velocity), the greater the water's capacity to create an impact when a valve is opened and the water (like electrons) can flow" and "The greater the voltage in a circuit, the greater its ability to "push" more electrons and do work" Agathiyar comes to enhance our storage capacity and upgrade the transformer station in readiness to receive the high pressure and voltage that is to come within us as we traverse higher altitudes heading for the summit and peak of God-realization. If he in preparedness for us to receive his grace brought us to his abodes that were power sources on earth, in the preparedness of us to receive the effulgence he moves within and clears the path of obstacles, widening it if necessary, and pushes us forward with an urgency. That is the grace of Agathiyar.