4.13 te vyakta suksmah gunatmanah
These (states) have manifested or subtle constituent forces of nature.
The forms of nature (prakrti) may be manifested (vyakta) or subtle (suksma). If an object can be perceived by the senses, we call it material or manifested. If an object cannot be perceived, it remains hidden or emerges later, then it is in a subtle state. Be it manifested or subtle, the object is composed of three constituent forces, or gunas of nature, namely sattva, rajas and tamas. Just like all colors in the world are made of three primary colors (red, green and blue), the three gunas are the primary constituents of all objects. In Sutra 4.12, Patanjali mentions that the existence of the past and the future is as real as that of the present. Past and future are due to different modes of manifestation of the gunas,
Sattva has the nature of pure, light, illumination or harmony. Rajas has the nature of activity, motion, movement or changing. Tamas has the nature of stability, stasis, darkness, dullness, heaviness and so on. When there is no manifestation of the universe, the three gunas are at equilibrium. Only when there are fluctuations or modifications, these gunas start to manifest. As the gunas change, various phenomena are produced in the universe.
Each guna does not stand on itself, but always mixes with the other two. However, at a particular time, a particular guna predominates. When sattva is predominating and rajas and tamas are under subordination, the person finds it easy to do concentration and meditation. When rajas is predominating, sattva and tamas are controlled, the person could still sit in meditative posture, but his mind is busy. When there is preponderance of tamas, the person get inertia and feels lazy to do action.
Having understood the three gunas, it is very common for practitioners to think that sattva should be increased. By increasing sattva, we can have brightness and brilliance in the face, lightness in the body, we feel pure, peace and illumination. However, yoga is not simply this. Yoga is a process of realization of liberation, kaivalya. Attaching to any of the gunas is not going to lead us to liberation. As a yoga practitioner, we should free ourselves from the cycle of gunas, go beyond our perceptions and understand that the essence of the universe remains the same. This is further explained in the next sutra, 4.14.