Yoga, the timeless science behind all true religions, consists of systematic and definite steps to realization of the soul's oneness with Spirit.
The Bhagavad Gita, which is a sacred dialogue between the divine teacher Krishna and his disciple Arjuna, is India's most beloved scripture of yoga, as explained in Paramahansa Yogananda's definitive two-volume translation and commentary: God Talks With Arjuna: The Bhagavad Gita — Royal Science of God-Realization.
The essence of the yoga path was set forth in systematic form by the ancient sage Patanjali in his short but masterly work, the Yoga Sutras. Paramahansa Yogananda has written:
"Patanjali's date is unknown, though many scholars assign him to the second century B.C. His renowned Yoga Sutras presents, in a series of brief aphorisms, the condensed essence of the exceedingly vast and intricate science of God-union — setting forth the method of uniting the soul with the undifferentiated Spirit in such a beautiful, clear, and concise way that generations of scholars have acknowledged the Yoga Sutras as the foremost ancient work on yoga."
The yoga system of Patanjali is known as the Eightfold Path, which leads to the final goal of God-realization.