Guru plays an important role in the life of devotees who seek truth from them and acquire much knowledge about the spiritual realm. They are able to shape their lives based on the teachings and advise of these gurus.
Gurus are considered to represent God himself. They are people who can lead one on the path of happiness and help in attaining salvation from worldly existence.
Guru Purnima is a festival traditionally celebrated by Hindus and Buddhists, marked by ritualistic veneration of the Guru, Guru Puja. Gurus are believed by many to be the most necessary part of lives.
This was the day the 'Adhi Muni' ('The first yogi' of this world. It is another name of god Shiva) teaches the yogic techniques to his seven students (Known as Saptha Rishi). In this day, this world got its first GURU. This day is very important to Hindus because this was the first day this humanity came to know that humans have ability to cross their limitation and also got the techniques to go beyond their five senses and can become enlightened Yogi. In ancient India guru Purnima was celebrated as a very big festival to remember the people about that the human have the ability to cross their limitation.
The day of Guru Purnima observed to the memory of the great sage Vyasa. All Hindus are indebted to this ancient saint who edited the four Vedas, wrote the 18 Puranas, the Mahabharata and the Srimad Bhagavata. Vyasa even taught Dattatreya, who is regarded as the Guru of Gurus.
By following his guidance, the disciples of Veda Vyasa grew to spiritual maturity and felt rich in gratitude to their teacher. Uncertain what form of thanks could possibly be adequate to express their gratitude, they asked Veda Vyasa himself, 'How can we repay you for the divine wisdom you have imparted to us?'
With great compassion, Veda Vyasa told his disciples that they could choose one day of the year to be especially dedicated to honoring Shri Guru as a way to express this profound gratitude.
The disciples of Veda Vyasa followed his guidance. They chose the full-moon day (purnima) of the month of Ashadha as it was the fullest and brightest of all the year's purnimas. This day became known as "Gurupurnima".
The Buddha went from Bodhgaya to Sarnath about 5 weeks after his enlightenment. Before Gautama (the Buddha-to-be) attained enlightenment, he gave up his austere penances and his friends, the Pancavaggiya monks, left him and went to Isipatana (Sarnath). He went to them because, using his spiritual powers, he had seen that his five former companions would be able to understand Dharma quickly. When Gautama Buddha found his five former companions, he taught them, they understood and as a result they also became enlightened. The sermon Buddha gave to the five monks was his first sermon, called the Dhammacakkappavattana Sutta. It was given on the full-moon day of Asadha.