This day is celebrated every year to express gratitude unto the Guru Principle. The ArchGuru, Sage Vyas (founder of the Guru-disciple lineage), is worshipped on this day. This festival is the greatest festival in the life of a seeker. Of course, even this celebration in gratitude to the Guru is done for the seeker's spiritual progress, since the Guru is a manifest form of The Lord Himself. Starting from Lord Shankara who is known as aadiguru and Shankaracharya in the middle and our current guru, i bow to all great Gurus in this world who are continuously imparting knowledge and wisdom to this manking. Gurubhyo namaha.