Firstly the term ‘Guru’ needs to be examined. The term 'Guru' in Sikhi is not used for a teacher or a guide or an expert or even a human body. The word Guru is composed of two terms:
GU – means darkness
RÛ – means Light
In Sikhi the word 'Guru' is, thus, defined as the Light that dispels all darkness, and that is called ‘Jyot’ (Divine Light). Guru Nanak Sahib Ji was, the True Guru (Satguru), the embodiment of Divine Light.
ਗੁਰ ਨਾਨਕ ਦੇਵ ਗੋਵਿੰਦ ਰੂਪ ॥੮॥੧॥
“Guru Nanak is embodiment of the Light of God.”
(Ang 1192)
In Sikhism the Guru is in whom the Light of God shines fully, visibly and completely. Guru is in union with Divine. Thus, ushers the devotee, the seeker of Truth into a spiritual birth. Through the True Guru the Glory of God is transmitted to humanity. Satguru is one with God and has existed since the start of time. Guru Nanak Sahib Ji is not a human but is in fact Shabad (Divine Infinite Wisdom).
ਦੂਜਾ ਨਹੀ ਜਾਨੈ ਕੋਇ ॥
ਸਤਗੁਰੁ ਨਿਰੰਜਨੁ ਸੋਇ ॥
ਮਾਨੁਖ ਕਾ ਕਰਿ ਰੂਪੁ ਨ ਜਾਨੁ ॥
ਮਿਲੀ ਨਿਮਾਨੇ ਮਾਨੁ ॥੨॥
"Let no one think that God and Guru are separate. The True Guru is the Immaculate Lord. Do not believe that He is a mere human being; He gives honor to the dishonored. ||2||"
(Ang 895)
This Shabad-Jyot (the Light) came into human form to reveal Naam to humanity, which is the only path to realise and merge into God and end the circle of birth, death, heaven and hell.
Do Sikhs have ‘Ten Gurus’?
There is ‘one’ Guru. The Ten were for explaining the completeness. The Ten figures are a complete figure.
Guru Nanak Sahib Ji took the form of Ten bodies. Bhatt Mathura Ji in Sri Guru Granth Sahib Ji clearly shows this:
ਜੋਤਿ ਰੂਪਿ ਹਰਿ ਆਪਿ ਗੁਰੂ ਨਾਨਕੁ ਕਹਾਯਉ ॥
ਤਾ ਤੇ ਅੰਗਦੁ ਭਯਉ ਤਤ ਸਿਉ ਤਤੁ ਮਿਲਾਯਉ ॥
“The Embodiment of Light, the Lord Himself is called Guru Nanak. From Him, came Guru Angad; His essence was absorbed into the essence.”
(Ang 1408)
The Ten Nanaks had one same universal message. They had a direct connection with the Divine. They don’t show you experience, rather they show you how to experience the Divine. The Shabad (Infinite Wisdom) is the True Guru, Satguru. And Satguru Nanak Sahib Ji is in essence the ‘Shabad’. Guru Nanak Sahib Ji and the Ten bodies revealed and interpreted the Shabad.
ਗੁਰ ਮਹਿ ਆਪੁ ਸਮੋਇ ਸਬਦੁ ਵਰਤਾਇਆ ॥
“In the True Guru (Nanak) You have installed Your own Spirit; You are pervading through the Word of Your Shabad.”
(Ang 1279)
There is only ‘One God’. A Sikh worships only the ‘One God’ and bows his or her head only to the Shabad (Infinite Divine Wisdom) which took the form of Ten Nanaks and was recorded in writing, which is the Sikh Guru today – Sri Guru Granth Sahib Ji, the revealed Divine Word of God.
