Because by reading about Yoga we are also practicing Yoga
The Yoga-sutras are ancient foundational texts of yoga, written in the form of aphorisms by the wise Patanyali in the 3rd century BC. C. The Yoga Sūtra is a guide, a map that the yogi uses to locate him/her self in his/her practice.
You can get the book with different comments about the Sutras, i recommend this one by Swami Shivananda.
Light on Yoga - B.K.S Iyengar
Thanks to this book Yoga arrived to many people`s everyday life. It includes a complete introduction to Yoga philosophy and practice, a full description of over 200 postures and pranayama techniques and over 600 photos .
What about the author?
Bellur Krishnamachar Sundararaja Iyengar, also known as Yogacharya B.K.S. Iyengar, was "Iyengar Yoga" founder. Considered one of the most important Yoga teachers in the world, he practiced Yoga for more than 75 years. He wrote many books about Yoga practice and philosophy. Some of them are : Light on Yoga, Light on Pranayama, Light on Patanjali Yoga Sutras.
Bhagavad Gita (2nd century BC) is one of the most important Hindu texts and it is written by an unknown author. Its about the conversation between Krishna and Arjuna on the battlefield during the moments just before the start of the Kurukshetra war. Responding to Arjuna's moral dilemma, Krishna explains to him his duties as warrior and prince, doing so with analogies of yogic and Vedantic doctrines.
Greg McKeown offers a framework for discerning what is essential, eliminating what is not, and removing obstacles in order to make the execution of what is essential as effortless as possible. The disciplined pursuit of less allows employees to channel their time, energy, and effort toward making the highest possible contribution to what really matters.
Body, mind and spirit
Yoga instructor Donna Farhi reveals how yoga enhances the connections between the mind, body, and spirit. She outlines the seven simple movement principles that underlie all human motion and provides exercises to help readers understand how they can achieve all yoga postures. She also discusses the ten ethical precepts that are the foundation of all yoga teachings and explains how to incorporate them into a spiritually and emotionally rewarding inner practice.