Yoga sutras Patanjali consist of 4 books; Samadhi Pada, Sadhana Pada, Vibhuti Pada and Kaivalya Pada. Samadhi Pada explain the basic of yoga. It is about the disciplines of yoga. As we know, yoga is all about mind and body. There are 3 criterias required in yoga practice, poses, breathe and also concentration. This is how we can re-establish the connection back to our bodies. Therefore this can be the most important and basic philosophy of the Yoga sutras Patanjali. Without these, yoga will be no different from other exercises.
The second book, Sadhana Pada, is about Kriya Yoga and also the eight limbs of yoga first described. The word Sadhana is practice in Sanskrit. Basically, this book is also about practice. Enlightenments and awareness of our being is the ultimate purpose in Krisya Yoga. This form of yoga is often practice by monk. Therefore, it is also often been related to Buddhism and Hindu.
Vibhuti is the word in Sanskrit for power. There are so many abilities described in the text that seem impossible to us now. But in fact Vibhuti Pada emphasizes to achieve full awareness of our bodies and awake of all senses. With the awareness, we can synchronize with the energy around us and achieve unity with the universe.
Kaivalya Pada, the book for isolation and freedom, is the last book in Yoga Sutras. How the mind works and the structure of it, is discussed in this book. All the physical being is manifest from our minds. Looking pass the physical being, we are just a pure consciousness of mind. This concept is very similar to law of attractions but it was told thousands years ago.
I have to emphasize here that yoga is not any exercise. The knowledge and wisdom behind all the poses is deep. It is design not only for our bodies but also for our minds. Maybe not everyone would like to achieve enlightenment now, but yoga practice will helps you to feel all your sensation again, reconnect you to your body and nature.