Time , place , circumstance
Guru Nanak is predicted by numerous vedic scriptures to come and spread this message of sikhism on Krishnas order , just like any other prophet in the past.
At that time in punjab many were involved in demigod and idol worship.
Therefore to benefit the persons of that time , the sikh relgion was to be formed. One god.
Lord Buddha had to deny the Vedas. So did Guru Nanak. Think about it ??
95 percent of his followers were hindu , how could they read the vedas and puranas and follow the sikh path at the same time -impossible. So the vedas were to be denied - to put their faith in god alone. Yes krishna is god sure , but jews , christians , muslims - the same circumstance. This message was particularly meant for the people at that time in punjab - to unite under one banner.
Putting aside the vedas , the sikhs could devote themselves to god , the supreme alone through bhakti.
The only debate would be about the mission of Guru Nanak to form to sikh relgion. Guru Nanak is simply a messenger for Lord Krishna. He was empowered - just read his life story. The following 9 gurus too were empowered souls to spread this message and also defend the vedic culture against the muslims.
An avatar must be predicted by scripture and so he was.
VAHEGURU - Vasudev Hari Govinda Ram - VAHEGURU
Krishna's name !!!! It is an ancient mantra found in vedic sciptures. Bhai Gurdas - a relative of 3 sikh gurus explains the mantra for us in his book Bhai Gurdas Varan - verse
Va - Vasudev
He - Hari
Gu - Govinda
Ru - Ram
It is an exceptionally powerfull mantra - the sikhs are also like us in spiritual bliss and ecstasy and those who are true follow the real regulations.
Vaheguru,Vaheguru,Vaheguru - beautifull mantra - beautifull sound - many sikhs have spoken of the bliss and ecstasy they feel from this mantra - the love mantra.
This was Guru Nanaks gift to the sikh people - sanctioned by Lord Chaitanya and Krishna.
Hare krishna ! Gauranga !