Masters are of four different types: The father, the mother, the preceptor or teacher, and lastly, Satguru (Spiritual Guide or Murshid-i-Kamil). Of all of these, Satguru is the greatest teacher, for he imparts spiritual instructions alone. One who is well-versed in worldly wisdom is called acharya or preceptor, for he gives us rules of social conduct and of ethical life. Satguru or Master of Truth is also known as Sant Satguru. His relation with his disciples is purely a spiritual one, as he is concerned with the advancement of spirit and has nothing to do with worldly matters.
From the viewpoint of spiritual attainments Gurus may be classified as:
Sant Satguru, and
Param Sant Satguru.
A Sadh is one who has gone beyond the region of Trikuti (Onkar) which is the same as Lahut in Sufi terminology and Hu in Islamic theology. He has witnessed the spirit in its pristine glory, after having rid it of all coverings, and is now Trigunatit (beyond the three gunas: Satva, Rajas, and Tamas, in which all human beings work according to their natural and native instincts); beyond the five elements (earth, water, fire, air and ether, of which the physical world is composed); beyond the twenty-five Prakritis (the subtle forms in varying degrees of the elements); and beyond also mind and matter. In short, he is an adept in self-knowledge, or the art and science of spirit, and can, at will, disengage the spirit from various koshas (sheaths or caskets) in which it is enclosed like a priceless gem. The greatness of a Sadh lies beyond the three gunas (as he is Trigunatit). By a process of self-analysis, he (a Sadh) has known the self or spirit in its real form-to wit, that it is of the same essence as God; and now he strives for God-knowledge.
A Sant is one who is adept not only in self-knowledge but in God-knowledge as well. He far transcends the material, materio-spiritual, and spirituo-material realms. Master of Truth as he is, his abode is in the purely spiritual region, technically called Sach Khand or Muqam-i-Haq, the Realm of Truth.
A Param Sant is the Grand Master of Truth beyond all description and hence ineffable. He is at one with what is variously known as Anami (The Nameless One) of Kabir; Nirala (Indescribably Wonderful), Mahadayal (Boundless Mercy) or Swami (The Great Lord of All).
There is no material difference between a Sant and a Param Sant except in nomenclature. But none of them, whether a Sadh, a Sant, or a Param Sant, can act or function as a Guru or Master unless he is competent to impart spiritual instructions and he has been commissioned from above to do this work. Whoever holds this authority for spiritual work becomes a Sadh Guru, Sant Guru or Param Sant Guru, as the case may be.
There may be a number of Sadhs, Sants or Param Sants, but none of them can of himself assume Guruship or spiritual preceptorship without being commissioned for the work.
So the terms Sadh, Sant and Param Sant have a much wider connotation than the term Guru, which is restricted to a spiritual preceptor alone - the rest being only spiritual adepts of varying degrees. The Guru holds a direct commission from God, and works under instructions just as any vice-regent would do on behalf of a king.
Again Gurus are of two types:
1. Swateh Sant Gurus: They are born Sants who come into the world with direct commissions; as for instance, Kabir Sahib and Guru Nanak.
They start the work of spiritual knowledge and instructions right from a tender age. They need no special training from anyone, since they come from the Most High for this purpose. Such beings, when they come, simply flood the world with the light of Spirituality, and establish a line of Gurmukh Gurus for carrying on the work long after them. But in course of time, substance comes to be sacrificed for show, and gradually Spirituality disappears altogether.
Then comes another Master Soul to re-orient this most ancient science according to the needs of the age. In this way, "old wine" remains in circulation for souls athirst. Such Master Souls do appear from time to time in different lands and among different peoples.
2. Besides Swateh Sants there are Sants who by devotional practice and spiritual discipline under the guidance of some Master Soul acquire spiritual merit here and are granted a commission to work as a Guru.