The principles of the yoga systems, karma-yoga, jñāna-yoga and haṭha-yoga, have some bhakti (devotion) added, as you can see from the practice that Om and Hare Krishna mantra are chanted by many teachers and students at Yoga studios in the U.S.; however pure bhakti-yoga, does not have any mixture of jñāna, karma or haṭha. Spirituality means something that pertains to the spirit. As eternal living entities we are spirit souls transmigrating from one body to other for a very long period of time. However, when in the human form we are given faculties to understand the purpose of life. As the student of yoga understands that the real purpose of life is to serve Krishna, he gradually gives up the lower forms of yoga such as karma-yoga, jñāna-yoga and haṭha-yoga and embraces devotional activities of Shravanam (hearing), Kirtanam (chanting and singing glories of God) which result in Vishnu Smaranam (remembrance of God’s presence in the heart along with the individual soul). Bhakti-yoga is very simple and pure and easy to perform. One can begin simply by chanting Hare Kṛṣṇa which unlocks the secrets to self-realization and God-realization. Lord Krishna also explains the “Art of Dying” which is to not attain a life again in this complex material world. In chapter 8.12, Lord says “After being situated in this yoga practice and vibrating the sacred syllable oṁ, the supreme combination of letters, if one thinks of the Supreme Personality of Godhead and quits his body, he will certainly reach the spiritual planets”. A pure devotee cannot forget the Supreme Lord for a moment, and similarly the Supreme Lord cannot forget His pure devotee for a moment. This is the great blessing of the Kṛṣṇa conscious process of chanting the mahā-mantra – Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare.