Passage quoted from BKS Iyengar

"Yoga is a light which, once lit, will never dim. The better your practice, the brighter the flame."

“If the foundation is firm, the building can withstand calamities. The practice of yoga is the foundation, so that the self is not shaken under any circumstances.”

"Yoga liberates you. When you practice yoga, your mind becomes unfettered and free. The impact of yoga is never purely physical. Asanas, if correctly practiced, bridge the divide between the physical and the mental spheres. Yoga stems the feelings of pain, fatigue, doubt, confusion, indifference, laziness, self-delusion, and despair that assail us from time to time. The yogic mind simply refuses to accept such negative emotions and seeks to overcome these turbulent currents on the voyage to the total liberation of the self. Once we become sincere practitioners of yoga, we cease to be tormented by these unhappy and discouraging states of mind. Yoga illuminates your life. If you practice sincerely, with seriousness and honestly, its light will spread to all aspects of your life. Regular practice will bring you to look at yourself and your goals in a new light. It will help remove the obstacles to good health and stable emotions. In this way, yoga will help you achieve emancipation and self-realization, which is the ultimate goal of every person's life."

“The conjunction of effort, concentration, and balance in asana forces us to live intensely in the present moment, a rare experience in modern life. This actuality, or being in the present, has both a strengthening and a cleansing effect: physically in the rejection of disease, mentally by ridding our mind of stagnated thoughts or prejudices; and, on a very high level where perception and action become one, by teaching us instantaneous correct action; that is to say, action which does not produce reaction.”

B.K.S. Iyengar,
The Yoga Sutras of Patanjali (1993)

“Through cultivation of friendliness, compassion, joy & indifference to pleasure and pain, virtue and vice respectively, the consciousness becomes favorably disposed, serene and benevolent.

This sutra asks us to rejoice with the happy, to be compassionate to the sorrowful, friendly to the virtuous, and indifferent to those who live in vice despite attempts to change them.”

B.K.S. Iyengar,
his commentary and translation: Yoga Sutra 1.33
The Yoga Sutras of Patanjali (1993)