Sikh religion is not the only one that places a great deal of importance on the Guru. Other religions call "Guru" by a different name.
Guru Nanak to Guru Gobind Singh Ji, and the jyot of all Gurus Guru Granth Sahib Ji, our present and forever Guru is for the Sikhs, what Jesus Christ is for the Christians, Lord Buddha for the Buddhists, and Mohammed for the Moslems. They are all Gurus for their respective followers.
No one is born with knowledge. It is acquired. We learn the 3Rs and science from our teachers in school. We learn spirituality from our Guru.
Guru is the facilitator between us mere mortals and our realization of the Lord God within us.
Krishna Singh Ji has explained this realization very nicely.