Savitri, Book Seven: The Book of Yoga, Canto IV: The Triple Soul-Forces.
Savitri arrives at the first three emanations or luminous powers that emerge from the soul, which support the physical, the vital and the mental nature from behind the human scene. These triple soul-forces are also sometimes known as the three gunas or modes of nature, tamas, rajas and sattwa. These powers have their divine origins as powers of peace and endurance (which changes into tamas), luminous force and strength (rajas), wisdom and balance (sattwa). Savitri observes each of these luminous powers and their corresponding shadows but rests not there. She must move further on.
