This is a post I wrote on another form a while ago. This might help. I do not claim to be 100% correct.
Satpurakh and SatguruNaam or Gurmantar is the Shabad Saroop of Waheguru that brings salvation and serves as the bridge between soul and Waheguru. Naam is obtained from Satguru. Gurbani says:
ਮੇਰੇ ਮੀਤ ਗੁਰਦੇਵ ਮੋ ਕਉ ਰਾਮ ਨਾਮੁ ਪਰਗਾਸਿ ॥
O my Best Friend, O Divine Guru, please enlighten me with the Name of the Lord.ਗੁਰ ਮੰਤ੍ਰ ਹੀਣਸ੍ਹ ਜੋ ਪ੍ਰਾਣੀ ਧ੍ਰਿਗੰਤ ਜਨਮ ਭ੍ਰਸਟਣਹ ॥
That mortal who lacks the Guru's Mantra - cursed and contaminated is his life.It is clear that Naam is important to get salvation and is only obtained from Satguru. Then who is Satguru? Satguru means True Guru like who there is none other. He alone is like Himself.
ਇਕੋ ਸਤਿਗੁਰੁ ਜਾਗਤਾ ਹੋਰੁ ਜਗੁ ਸੂਤਾ ਮੋਹਿ ਪਿਆਸਿ ॥
Only the Guru is awake; the rest of the world is asleep in emotional attachment and desire.ਇਕਾ ਬਾਣੀ ਇਕੁ ਗੁਰੁ ਇਕੋ ਸਬਦੁ ਵੀਚਾਰਿ ॥
There is One Bani; there is One Guru; there is one Shabad to contemplate.There is only One True Guru in the world. He alone is always awake. He is not in the cycle of death and birth.
ਸਤਿਗੁਰੁ ਮੇਰਾ ਸਦਾ ਸਦਾ ਨਾ ਆਵੈ ਨ ਜਾਇ ॥
My True Guru, forever and ever, does not come and go.There is only One Satguru who gives naam and He never takes birth and therefore never dies. There have been many prophets, messengers, angels and what not but they all took birth and died. Neither did they ever give naam nor were they given the status of Satguru. There have been, are and will be many self-styled Gurus but only One is given the status of Satguru by Waheguru and that is Guru Nanak Sahib. He is the greatest of all and the true savior.
ਸਭ ਤੇ ਵਡਾ ਸਤਿਗੁਰੁ ਨਾਨਕੁ ਜਿਨਿ ਕਲ ਰਾਖੀ ਮੇਰੀ ॥4॥10॥57॥
Guru Nanak is the greatest of all; He saved my honor in this Dark Age of Kali Yuga. ||4||10||57||Satguru Nanak Sahib did not take birth but emerged in the world.
ਸਤਿਗੁਰ ਨਾਨਕ ਪ੍ਰਗਟਿਆ ਮਿਟੀ ਧੁੰਧ ਜਗ ਚਾਨਣ ਹੋਆ॥
With the emergence of the true Guru Nanak, the mist cleared and the light scattered all around.He appeared in Sargun form in the world. He has been Satguru since the beginning. Bhatts say:
ਤੂ ਸਤਿਗੁਰੁ ਚਹੁ ਜੁਗੀ ਆਪਿ ਆਪੇ ਪਰਮੇਸਰੁ ॥
You are the True Guru, throughout the four ages; You Yourself are the Transcendent Lord.Hence it is clear that Guru Sahib, the jot saroop of Waheguru, is the Satguru of all ages and times. He was already a Satguru when appeared before the world and fog of ignorance and false rituals disappeared. All Bhagats, saints, yogis and others who did bhagtee were not Satguru since there can only be One Satguru.
Some Sikhs use the panktee in Sukhmani Sahib to justify that Satguru can be anyone.
ਸਤਿ ਪੁਰਖੁ ਜਿਨਿ ਜਾਨਿਆ ਸਤਿਗੁਰੁ ਤਿਸ ਕਾ ਨਾਉ ॥
The one who knows the True Lord God, is called the True Guru.ਤਿਸ ਕੈ ਸੰਗਿ ਸਿਖੁ ਉਧਰੈ ਨਾਨਕ ਹਰਿ ਗੁਨ ਗਾਉ ॥1॥
In His Company, the Sikh is saved, O Nanak, singing the Glorious Praises of the Lord. ||1||Although it is clear from the Saloak and the remaining Aastpaddi that the panktee refers to fourth embodiment of Guru Nanak Sahib. Words Brahmgyani, Sant, Sadh, Satgur etc all refer to Guru Raamdas Ji who is satsaroop of Guru Nanak Sahib. Some panktees make it crystal clear who Satguru is:
ਸਤਿਗੁਰੁ ਸਿਖ ਕਉ ਨਾਮ ਧਨੁ ਦੇਇ ॥
One who gives naam is Satguru. As shown above only Satguru has that right and He is only One. Some more panktees make it clear that Satguru cannot be just anyone.
ਗੁਰ ਕੀ ਆਗਿਆ ਮਨ ਮਹਿ ਸਹੈ ॥
ਮਨੁ ਬੇਚੈ ਸਤਿਗੁਰ ਕੈ ਪਾਸਿ ॥
Above two panktees prove that a Sikh or a devotee must give up his own mind and obey the hukam of Guru. In Anand Sahib, similar instruction is given to Sikhs
ਤਨੁ ਮਨੁ ਧਨੁ ਸਭੁ ਸਉਪਿ ਗੁਰ ਕਉ ਹੁਕਮਿ ਮੰਨਿਐ ਪਾਈਐ ॥
Surrender body, mind, wealth, and everything to the Guru; obey the Order of His Will, and you will find Him.
Who is the Satguru that Guru Arjan Sahib Ji is talking about? He says:
ਬੀਸ ਬਿਸਵੇ ਗੁਰ ਕਾ ਮਨੁ ਮਾਨੈ ॥
ਪੂਰਾ ਗੁਰੁ ਅਖ੍ਹਓ ਜਾ ਕਾ ਮੰਤ੍ਰ ॥
That Satpurakh is Poora or complete. “Bees Bisvai” means someone who is undoubtedly a complete Guru. Second line says that Satguru is Poora Guru who gives Gurmantar which must be chanted by the Sikhs (followers). One most important line in the entire shabad is the following:
ਨਿਰਗੁਨੁ ਆਪਿ ਸਰਗੁਨੁ ਭੀ ਓਹੀ ॥
Satguru is Nirgun and Sargun. Now, it becomes clear that Satguru cannot be any human being, prophets or bhagat since none of them were nirgun. Nirgun is only Waheguru and His Sargun saroop is Guru Nanak Sahib. None other can ever get this status. Some will still doubt that Bhagats who became mukat or achieved salvation refer to their respective Gurus as Satguru but this is false as the following panktee makes it clear:
ਅਨਿਕ ਭਗਤ ਬੰਦਨ ਨਿਤ ਕਰਹਿ ॥
Countless Bhagats including Ramanand, Kabir, Farid, Dhroo, Prehlaad and others revere and sing glorious praises of Satguru. Besides, it has been shown above that Satguru Guru Nanak Sahib is the greatest of all. Since He is the greatest none other can become equal to Him.
Some gullible Sikhs may still doubt that other Bhagats can reach the status of Satguru. Many scholars give the meanings of the saloak the same way but none have explained the essence behind it. As far as I know only Bhai Randhir Singh Ji has explained the implied meaning behind this saloak. The following is based on his work:
To know the Satpurakh completely is impossible for the humans. They can only realize Him and follow His Hukam. To claim to have known Him is a blasphemy. Only Waheguru Himself knows His greatness. Many claim to have known Him for the sake of calling themselves Gurus but they are nothing but fake. For such people Guru Sahib says:
ਅੰਤ ਕਾਰਣਿ ਕੇਤੇ ਬਿਲਲਾਹਿ ॥ ਤਾ ਕੇ ਅੰਤ ਨ ਪਾਏ ਜਾਹਿ ॥
ਏਹੁ ਅੰਤੁ ਨ ਜਾਣੈ ਕੋਇ ॥ ਬਹੁਤਾ ਕਹੀਐ ਬਹੁਤਾ ਹੋਇ ॥
Many struggle to know His limits, but His limits cannot be found. No one can know these limits. The more you say about them, the more there still remains to be said.
He is so great that more one praises Him less and less it gets. In other words, His praises will never be enough and more one praises greater He becomes and gets.
ਅਤਿ ਊਚਾ ਤਾ ਕਾ ਦਰਬਾਰਾ ॥ ਅੰਤੁ ਨਾਹੀ ਕਿਛੁ ਪਾਰਾਵਾਰਾ ॥
ਕੋਟਿ ਕੋਟਿ ਕੋਟਿ ਲਖ ਧਾਵੈ ॥ ਇਕੁ ਤਿਲੁ ਤਾ ਕਾ ਮਹਲੁ ਨ ਪਾਵੈ ॥1॥
His Darbaar, His Court, is the most lofty and exalted. It has no end or limitations. Millions, millions, tens of millions seek, but they cannot find even a tiny bit of His Mansion. ||1||
There are no limits. He is beyond time and form. He is timeless form that has neither beginning nor end. How could human creatures that hardly live for 100 years get to know Waheguru or realize His limits since He is beyond time? Knowing the timeless is not possible for those under the influence of time. Those who born and die can never be at that level. To realize Him or know Him, one must also be beyond time and as great as Him. Only a Satguru has that level since Satguru is beyond the cycle of death and birth. Satguru, Sargun Waheguru, is also beyond time. Gurbani says:
ਵਡਾ ਸਾਹਿਬੁ ਊਚਾ ਥਾਉ ॥ ਊਚੇ ਉਪਰਿ ਊਚਾ ਨਾਉ ॥
ਏਵਡੁ ਊਚਾ ਹੋਵੈ ਕੋਇ ॥ ਤਿਸੁ ਊਚੇ ਕਉ ਜਾਣੈ ਸੋਇ ॥
Great is the Master, High is His Heavenly Home. Highest of the High, above all is His Name. Only one as Great and as High as God can know His Lofty and Exalted State.Many prophets, bhagats and others can never be Satguru Waheguru Himself knows His greatness. None other have been, are or will ever be as great as Waheguru. Those who make such claims are “Moorakh Sir Moorakh” and “Gaavara Gaavaar”. Many Sikhs during the time of Guru Sahib and afterwards were blessed with visions of Waheguru and had all the powers in the world but none ever dared to call themselves Satguru. No Sikh ever gave naam to others. Baba Buddha Ji was a great Sikh scholar and none other could match his knowledge yet he was humble and always remained the servant of the Guru. He never made any claims. True Sikhs know that all the blessings are obtained by the grace of the Guru. Therefore, they always submit themselves to the Guru. They never considered themselves equal to the Guru because they were Sikhs not Satguru. Satguru is always the greatest. Naam from Satguru merges one with Waheguru but naam doesn’t make anyone Waheguru. Like a drop of water merges with the ocean but that drop itself is not an ocean. It is the greatness of the ocean to merge the drop of water but then the drop would not exist.
Those who claim to know the Waheguru and call themselves Satguru are false and Gurbani says:
ਸੋਈ ਅਜਾਣੁ ਕਹੈ ਮੈ ਜਾਨਾ ਜਾਨਣਹਾਰੁ ਨ ਛਾਨਾ ਰੇ ॥
One who claims to know, is ignorant; he does not know the Knower of all.Only Satguru Nanak Sahib is the knower of Waheguru since He is Waheguru Himself. True Sikhs always long for Gurmat and wish to remain in the feet of the Guru. Those who have the desire to call themselves “Sants/Brahmgyanis” and seek followers will never achieve anything. Sikh is always a Sikh. There is no place for Sants in Sikhi since every Sikh is a Sant and Sipahi. Those who do naam abhiyaas and reach higher spiritual state ware also Sikhs and do not become higher than other Sikhs. Being the son of Guru Sahib should be more than enough. Only egomaniacs and pakhandis leave Sikhi and seek special status. In Gurmat there is only Guru and Sikh. Only Guru Sahib knows the Satpurakh Waheguru. He is the greatest of all and none else will ever be like Him.
ਸਚੁ ਸਚਾ ਸਭ ਦੂ ਵਡਾ ਹੈ ਸੋ ਲਏ ਜਿਸੁ ਸਤਿਗੁਰੁ ਟਿਕੇ ॥
ਸੋ ਸਤਿਗੁਰੁ ਜਿ ਸਚੁ ਧਿਆਇਦਾ ਸਚੁ ਸਚਾ ਸਤਿਗੁਰੁ ਇਕੇ ॥
ਸੋਈ ਸਤਿਗੁਰੁ ਪੁਰਖੁ ਹੈ ਜਿਨਿ ਪੰਜੇ ਦੂਤ ਕੀਤੇ ਵਸਿ ਛਿਕੇ ॥
ਜਿ ਬਿਨੁ ਸਤਿਗੁਰ ਸੇਵੇ ਆਪੁ ਗਣਾਇਦੇ ਤਿਨ ਅੰਦਰਿ ਕੂੜੁ ਫਿਟੁ ਫਿਟੁ ਮੁਹ ਫਿਕੇ ॥
ਓਇ ਬੋਲੇ ਕਿਸੈ ਨ ਭਾਵਨੀ ਮੁਹ ਕਾਲੇ ਸਤਿਗੁਰ ਤੇ ਚੁਕੇ ॥8॥
The True Lord is truly the greatest of all; he alone obtains Him, who is anointed by the Guru. He is the True Guru, who meditates on the True Lord. The True Lord and the True Guru are truly One. He is the True Guru, the Primal Being, who has totally conquered his five passions. One who does not serve the True Guru, and who praises himself, is filled with falsehood within. Cursed, cursed is his ugly face. His words are not pleasing to anyone; his face is blackened, and he is separated from the True Guru. ||8||Waheguru Ji Ka Khalsa Waheguru Ji Ki Fateh
ਸਤਿਗੁਰਬਚਨਕਮਾਵਣੇਸਚਾਏਹੁਵੀਚਾਰੁ॥