There are many relationships in the world surrounding us like father, mothers,uncle,friend etc. Forming yet another relationship with a Guru, is no different.If the parents are the 1st guru of the children then why there is need for a guru again.
Bhagbat Gita CH-18,verse-66 tells us :-Abandon all varieties of religion and just surrender unto Me. I shall deliver you from all sinful reaction. Do not fear.
if a person surrender himself to god it manifest god is guru then why again there is need for guru..!