Sruti Gita is from the Srimad Bhagwat and reveal the nature of the Nirgua Brahman - beyond the rajsik, tamsik and satvik. How mind accesses Absolute Truth, indescribable by material words, totally devoid of material qualities and how liberation can be achieved.
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.