In sūtra 2.32, Rishi Patañjali writes:
śauca saṁtoṣa tapaḥ svādhyāya īśvarapraṇidhānāni niyamāḥ
While yama demands control over external behaviors, niyama focuses on the inner life of the yogi: śauca (purity), saṁtoṣa (contentment), tapaḥ (self-discipline), svādhyāya (self-study) and вśśvara-praṇidhānāni (faith, love and devotion to God) are the virtues that the yogi should acquire.
Swami Vivekananda says: “A dirty person will never become a yogin” – śauca, physical and mental purity, is a prerequisite for the success of the yoga practice.
Saṁtoṣa or contentment means for the yogi to renounce worldly desires. Only then can he achieve a balanced and contented state of mind, in success and failure, in joy or sorrow.
The bhagavad gītā (śloka 17.14 to 17.17) requires tapas or self-discipline on three levels: physically, tapas corresponds approximately to the yamas in Patañjalis sūtra 2.30; Tapas demands that the speech be true and kind and that the scriptures should be recited; Spiritual self-discipline includes self-restraint, spiritual calm, and purity of being. Without self-discipline, the other elements of yama and niyama are not possible.
Self-study (svādhyāya) includes the study of physiology, psychology and philosophy. But also the study of one’s own soul in meditation belongs to svādhyāya.
Jesus best showed what īśvarapraṇidhānāni means when he said, “Father, your will be done.” Faith, love and devotion to God are the key to success in yoga. If the yogi is in doubt or can not subordinate his own will to the higher will of God, he remains trapped in his human existence. Only when he surrenders and can accept the divine will, he achieves peace and perfection in meditation.