The term 'twofold nature' refers to the concept of DUALITY or dualism. DUALITY is the idea that two seemingly opposite forces can exist together, while dualism is the belief that two distinct and separate entities can coexist. This concept has been explored in many different contexts, from philosophy to religion to science. In philosophy, it is often used to explain the relationship between mind and body, or between good and evil. In religion, it is used to describe the relationship between God and man. In science, it is used to explain the relationship between matter and energy.