Prakriti and Purusha
Know that prakriti (nature) and purusha (spirit) are both beginningless; and know that modifications and the gunas arise from prakriti.
The Samkhya philosophy underlying the Gita distinguishes between prakriti (material nature, the field) and purusha (pure consciousness, the knower). Both are eternal; their interaction produces the manifest world. Prakriti provides the material; purusha provides the awareness. Understanding this duality is the first step; transcending it in non-dual realization is the goal. The Self is neither nature nor spirit exclusively but the ground of both.
Material nature and the living entities should be understood to be beginningless. Their transformations and the modes of matter are products of material nature.
Samkhya provides the analytical framework; Vedanta provides the synthesis—ultimately prakriti and purusha are not two but manifestations of one reality.
Bhagavad Gita