What is meaning of Guru ?
The person who give teachings to their followers. As guru granth sahib ji is teacher of all their followers and treated as shabad guru.
Guru nanak dev ji preach akal pukh almighty God thus he is disciple of God mean Bhagat of akal purkh same in case of all gurus . All gurus are bhagat of akal purkh but they are gurus for us
Likewise all the Bhagats are preacher of almighty God that's why they are bhagat of God not any other , and they are guru for those who follow their teachings
Guru Granth Sahib has teachings of many Bhagats and gurus . We gain the teachings from guru granth sahib ji that's why the people who has bani in guru Granth Sahib Ji treating as Guru
If someone said Bhagats are unable to do something they blaming all the Guru Granth Sahib Ji
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