The Guru Granth Sahib is considered as the 11th Guru and final Guru of the religion. It is the only such document in the whole world which has the status of a Guru and is considered as the Supreme Spiritual Authority and Head of the Sikh religion as opposed to having a living person which is the norm in most of the religions. It is believed that the holy spirit of the Gurus and the authority got transferred into this scripture after the 10th Guru – Guru Gobind Singh. It is also unique as it not only contains the works of the Sikh Gurus but also of those of people belonging to other faiths.
Guru Nanak manifested the Word of God on Earth through his hymns and prayers (Shabads) and inspired the fellow Sikhs to lead a life of truth, righteousness and spirituality. In his last years at Kartarpur it became customary to sing these hymns – Japji in the morning, So Dar and So Purakh, the beginnings of Rehiras, in the evenings.
Guru Angad, Guru Amar Das, Guru Ram Das and others composed these Shabads and the small books of these compilations, called Pothis, were collected by the Sikhs.
Guru Arjan Dev, the fifth Sikh Guru, compiled all the Shabads into a single volume, the Adi Granth in 1604 in the city of Amritsar and installed it in the Golden Temple. He also added some of his own and hymns from other faiths which reflects the core principle of Sikhism – One God, One Family of Humanity and that all are children of God
But history has it that, Dhir Mal, grandson of Guru Hargobind refused to give the Adi Granth to Guru Gobind Singh and ridiculed him by saying “If you are a Guru, then prepare your own.” Guru Gobind Singh was no ordinary and in those days oral traditions had much more emphasis than physical documentations. Guru Gobind Singh dictated the entire Granth to Bhai Mani Singh who documented this on paper and finally completed rewriting the entire Granth by 1705. He did not record his own Shabads in the Granth but placed them in a separate Granth called the Dasam Granth which doesn’t have the status of a Guru.
Guru Gobind Singh then installed the entire re-written Adi Granth in Nanded ( on the banks of Godavari, Maharashtra) as the GURU on October 20th, 1708 and this day is celebrated as Guru Gadi Divas (Enthronement Day)