Guru Nanak

"....the Primal Master is always placed in looking after our Void, in sustaining us, and giving us a model of an ideal master. And he always took birth either in the most difficult places like hills and dales and mountains, or they took places - which are even more difficult thing, among the people who were horrid, and who needed their help. So in India, that time somehow Punjab was regarded as the place where people did not respect God or traditional Hindu idols, or you can say the statues that were regarded as the vibrating ones. But they worshipped money (even now) and they worshipped power. And as at that time there was a King who was very anxious to convert people to Islamic religion by giving them money, many were taking to Islam. As a result the Hindus started hating the Muslims and a big hatred developed among Muslims and Hindus. That's how, in those circumstances where there was a quarrel going on between the followers of Mohammad and followers of Hinduism, Mohammad himself took his birth on this earth, though he had decided not to take any more births, he thought that it would solve the problem. Although, this incarnation is such that it never dies. Even if they leave the body, they are always around. And they are the ones who perform lots of miracles when any other incarnation comes on this earth. They help support and guide the seekers to go to the incarnations. So, to celebrate his birthday on such a date is also a myth, because he never died. He is eternally living. They never grow and they never die.
But his birth is important, because symbolically he came on this earth not to propagate any particular type of the void - as Mohammad did or say Moses did, and before that Abraham, Lao Tse, or Socrates - which followed into a religion. But he came to create amity - we can say, to create understanding, to create unity between religions. This was a very big step for Sahaja Yoga."
(H.H.Shri Mataji Nirmala Devi, Talk on Nanak's Birthday, London, 1/11/82)

Source: guru-nanak.blogspot.com