The Bhagavad Gita tells us that humans, as well as all other things in Nature, have a mixture of Sattwa, and its companions, Rajas and Tamas. These three Maha Gunas (qualities) determine our behavior, actions, thoughts and emotions.
Sattwa is clarity, light, purity and wakefulness. It is stability, essence, compassion and love. Sattwa is required for our mental and physical health, and is the path to personal evolution and spiritual maturity.