Sanatan Gita (Eternal Song) teaches about Universe, life, atma, humanity, divinity and the primary three basic energies (Tamsik, Rajsik & Satvik).
Gita and Ramayana are perhaps the sum total of the fabrics of Hinduism (a way of life).
The Gita (song) are teaching by Divine or ancient revered holy rishis teaching both metaphysics and practice of disciplined action. They proclaims that life is worth living, teaches how it should be lived and the path to self-realisation. They are the cream of the Upanishads, which themselves are the core of the Four Vedas.