1.15. Desirelessness towards the seen and the unseen gives the consciousness of mastery.
1.16. This is signified by an indifference to the three attributes, due to knowledge of the Indweller.
1.17. Cognitive meditation is accompanied by reasoning, discrimination, bliss and the sense of 'I am.'
The spiritual path is an individual journey. Yoga intends, as it's goal, to reach the end of that path. Sometimes when we begin Yoga, the practice can be more painful then pleasurable because we become aware of things about ourselves we may not like. Think of it as a mirror being held up in front of you to show you your true self. Digging into the consciousness can make us hit the proverbial sewage line, but these Sutras tell us to keep digging until we reach the vein of gold. Even at that point, we must keep digging until we transcend all desire.
Sutra 1.15 emphasis desirelessness. Desire is a cause of suffering. When we are in a state of want, we set ourselves up for a state of lack. I think the game of life is rigged so that our material cravings can never be satisfied. Our economy is based on the idea of novelty. The marketing and sales industry have used this to drive our consumerist habits for better or worse. Spiritual seekers often get stuck along the side of the road during their journey. One day, we reach a profound understanding, only to have it taken away. Disirelessness is reached through detachment, which leads to mastery of practice
1.16 is a direct reference to the three gunas. The gunas are fundamental attributes that make up material existence. They weave themselves through the universe like a cosmic tapestry, maybe more like a hammock that we lay ourselves upon.
Tamas represents inertia, dullness, darkness and ignorance. It does not necessarily mean "evil" in the traditional sense.
Rajas is the activated state of matter. This attribute is active, fiery, and listless.
Satva is the higher state of being. It represents purity. balance and order.
Matter, as taken in Samkya Yoga philosophy, is a mixture of this states. Think of Rahas like a pendulum that swings between Tamas and Sattva.
1.17 get's into the "I am-ness" of things. "I am" has the deepest connotation in Yoga. It's the goal, the end of the road, the realization that I am. It's the part of the larger whole, or that pure, untainted consciousness the Yogi strives for. Abrahamic religions use the word Amen or Ahmeen as an affirmation of truth at the end of a prayer. In Sanskrit Aham means "I-am". See the correlation?
One of my Gurus, Goswami Kriyananda put these three sutras into an elegant metaphor: Think of the mind as a glass jar full of marbles. Some of these marbles are colored back, some red and some white. Red represents Rahas, Black Tamas and White Satva. All of our jars are a mixture of marbles of differing combinations. When practicing Yoga, we try to replace the black marbles with red ones, then the red ones with white ones. At the end of the journey, we dump the jar out. The glass jar represents pure consciousness, with the clarity to see things as they are, unencumbered by the weight of the marbles.