Bhagavad Gita was rendered by none other than Bhagavan himself. In Hindu culture, thousands of years ago, we already had the concept of working like Wikipedia. The ultimate knowledge is known only to people who were self-realized, who used to be known as Rishis. The seers, who experienced ultimate knowledge and decided to share it in some form left behind the scriptures and works for the larger benefit of humanity.
Viewed in that sense, Hindus are not guided by any one scripture and the treasure of knowledge is mind-blowing to say the least. The unique distinction of Bhagavad Gita is that it was rendered by none other than an avatar of Narayana himself and as Swami Vivekananda himself explains, ordinary humans in today's age cannot fathom how someone like Krishna lived and walked on earth. He was a super human personality that inspires awe to this age.
Krishna paramatma spelt out Gita in a battle context and therefore it took a certain form and shape. The principles enunciated by Gita re-inforce the messages earlier laid out in Vedas and Upanishads and helps understand them deeper. However, it's not possible to understand the true meaning and depth in one reading and perhaps through one translation. It takes dedication and humbleness to understand the nuances of what Krishna says.