To understand the answer to this question, we first need to know that within our physical body, we have a subtle physiology. There are energy pathways, called nadis or meridians that are connected with the different energy centers (chakras) that go from the base of the spine to the top of the head (the Bhramarudra). This subtle body is not as subtle as the mind, but is more subtle than the veins that the blood runs through. The primary meridians that the energy runs though are pingala (the right channel at the end of the right nostril) and Ida (the left channel). These two meridians, just like blood vessels, circle around and end at the base of the spine, going into the main meridian, called the sushumna. The idea of pranayama is to clear these meridians by doing alternate breathing. Generally, this is accomplished by breathing through one nostril, then the other. The idea of the hatha yoga system is to clear all the little meridians - similar to acupuncture - but done by using the breath and ability to concentrate, to make it so that the energy and mind are flowing through this middle channel. The sushumna is like a hollow bamboo tube for the energy to flow through - except that in most people, it is not hollow anymore, as it has blocks along the way .
Asana and pranayama yoga are mechanical processes, efforts to influence oneself to be more in the mode of goodness - to eventually have the mode of goodness be more dominant than the other material modes of nature (gunas). A person uses pranayama breathing to make it so that these two nadis or meridians (one associated with the mode of passion and the other associated with the mode of ignorance) both start entering into the sushumna at the base of the spine - which is associated with the mode of goodness. The purpose here is to purify one's consciousness through a mechanical method of manipulating the meridians or nadis. It is simply a mechanical process, connected to the three gunas (material modes of ignorance, passion, and goodness). This is also the purpose of yoga asana. When you are twisting this way and that way, just as you are opening up certain muscles, joints, and veins, you are simultaneously opening up these meridians - so that all the meridians, all the prana, can all be flowing ultimately more freely through the main channel, the sushumna, between the base of spine to the top of the head. That is the purpose of asanas and the purpose of pranayama. They are mechanical processes to try to purify oneself from the influence of the modes of ignorance and passion so one is more situated in the mode of goodness. A person moves more into the mode of goodness as more prana is moving though the sushumna.
However, in this age of Kali Yuga, where human beings have less attention and ability to dedicate their lives in pursuit of self-realization because of the distraction of the modern world all around us, these means of purification are not the recommended methods.
Fortunately for the sincere seeking soul, the good news is that there is a much easier process available to us. The recommended path of Yoga for this day and age is that of Bhakti-Yoga, Bhakti means love and Yoga means to link, unite, or yoke-up (as in yoking a bull to a cart). So, Bhakti Yoga means Loving Union with the Supreme Soul. In practice, Bhakti-Yoga is developing our loving connection with the Supreme through practical methods which engage all of our external senses. The simple actions that we already perform in our daily lives - such as eating, singing, dancing, etc - can all be dovetailed to nurture and further develop our Bhakti, or loving devotion to the Supreme.
The easiest method of meditation is that of mantra meditation, or kirtan. What is kirtan? Kirtan is the hearing and repeating of mantras in a group - two or more people gather together and sing the sacred sounds to music. Mantras are transcendental sound vibrations which are Sacred Names of the Supreme Person. Just as we have many names (i.e. Mom, Radha, Dear, Honey, etc), God has many Names. And in the process of Bhakti Yoga any Name of God is accepted as a purifying mantra - Krishna, Govinda, etc., any name of the Supreme Person can be called upon. Just as a waterfall is cleansing to the person who stands under it, the process of mantra meditation, or kirtan, works to cleanse away our materially contaminated consciousness - revealing our truest spiritual nature, bringing us back to our self. Kirtan is a joyful, uplifting method of meditation where one can very easily focus ones mind and quickly reach a deep meditative state, one-pointedly immersed in higher consciousness. When one sings kirtan with an open heart, their Bhakti naturally grows and develops.
I invite you to join us for a community candlelight kirtan, where you can immerse yourself in the sacred sounds and experience kirtan for yourself. In Hawaii, we offer regular kirtan events, private gatherings, and annual Kirtan Yoga Retreats. We invite you to join us on the beautiful island of Kauai for a full immersion in this wonderful Yoga practice.