These forms are manifest or subtle and composed of the material modes of Nature (Gunas).
Everything whether manifest (effect) or subtle (cause) is made up of the material modes of Nature (Gunas). The material modes of Nature are the qualities of Tamas or inertia /statis, Rajas or activity / force of mutation and Sattva or balance / sentience.
Our moods, thoughts and actions are driven by the material modes of Nature in the space-time continuum that the body-mind complex experience as daily life. Being caught and absorbed in this cycle of the Gunas in a series of moments that we delineate as past, present and future is called being trapped on the wheel of Samsara.
You are not your body nor mind. Identifying with our body or mind is called misidentification and operating in the mode of ignorance. You are the Atman, the Spirit Soul. Identifying with / knowing the Atman is operating from our true constitutional position. It is Self-knowledge or knowing the Self.