Guru Nanak was a reformer and not a revolutionary.

1. GN's was opposed the caste system but it was so mild that it never attracted any opposition from the other caste. Probably they agreed with him.
2. GN's denouncement fasts, penances, piligrames implied attack on perversions and not on the basic tenets of Hinduism. Fasts were only a means to an end and not an end to themselves.
3. GN never depreciated the Vedas. He criticized the blind and mechanical reading of these texts without realizing the God through them.
4. Even the Sacred Thread was not wholly condemned. He denounced the ignorance of the implications of its use.
5. While challenging the predominant position of Hindu deities, GN did not hold them in any disrespect. He wanted people to realize that they were not above God.
6. GN suggested no further change in the civil institution of Hinduism.

In short GN was a reformer like many others who preceded and followed him. The concept of love and devotion preached by him found wide acceptance. Khalsa was the result of Mughal tyranny. The five K's were used to identify people who supported GGS in his fight against the Mughals.