"Among the 12-13 full moons in a year the vaishakha full moon is dedicated to Buddha (his birth and enlightenment), jyeshtha full moon to mother earth and the aashadha full moon is dedicated to the memory of masters. This is Guru-Purnima.
It is the day when the disciple wakes up in his fullness and in the wakefulness he can't be but grateful. This gratitude is not of dwaita (you and me), but of advaita. It is not a river moving from somewhere to somewhere, but is the ocean moving within itself. So, gratefulness on Guru-Purnima symbolizes that fullness.
The purpose of the Guru Purnima celebration is to turn back and review and see in this last one year how much one has progressed in life. For a seeker, Guru Purnima is a day of significance. It is the day to review one's progress on the spiritual path and renew one's determination and focus on the goal. As the full moon rises and sets, tears of gratitude arise and repose into the vastness of one's own self."