Accepting pain as help for purification, study of spiritual books and surrender to the Supreme Being constitute Yoga in practice.
Yoga in the form of action (kriya yoga) has three parts: 1) training and purifying the senses (tapas), 2) self-study in the context of teachings (svadhyaya), and 3) devotion and letting go into the creative source from which we emerged (ishvara pranidhana)
This sutra describes yoga in action. The first of the 3 components is tapas, which is often mistranslated as ‘austerity’. It actually refers to creating heat, which purifies. Tapas also refers to self discipline – taming the monkey mind, the senses and the organs. Satchidananda quotes the Bhaghavad Gita which says that self-torture is an obstacle to spiritual progress, but self-discipline is an aid to it.
Self-study refers to reading some scriptures – these sutras, the Bible, the Koran, the Bhagavad Gita, the teachings of Zen Master Dogen – whatever resonates with you.
Surrendering to the supreme being or god is the third part of yoga in action. As a Buddhist and an atheist, I find this type of statement difficult. As with earlier notions like this, I will substitute ‘universal energy’ for the idea of ‘god’. This helpful blog says that the concept of ishvara could mean ‘collective consciousness’ or ‘universal consciousness’, rather than a ‘god’ deity.