The Chakras are centres of Shakti as vital force. In other words, these are centres of Pranashakti manifested by Pranavayu in the living body, the presiding Devatas of which are the names for the Universal Consciousness as It manifests in the form of these centres. The Chakras are not perceptible to the gross senses. Even if they were perceptible in the living body which they help to organise, they disappear with the disintegration of organism at death.
Purity of mind leads to perfection in Yoga. Regulate your conduct when you deal with others. Have no feeling of jealousy towards others. Be compassionate. Do not hate sinners. Be kind to all. Success in Yoga will be rapid if you put your maximum energy in your Yogic practice. You must have a keen longing for liberation and intense Vairagya also. You must be sincere and earnest. Intense and constant meditation is necessary for entering into Samadhi.
The mind of a worldly man with base desires and passions moves in the Muladhara and Svadhishthana Chakras or centres situated near the anus and the reproductive organ respectively.
If one’s mind becomes purified the mind rises to the Manipura Chakra or the centre in the navel and experiences some power and joy.
If the mind becomes more purified, it rises to the Anahata Chakra or centre in the heart, experiences bliss and visualises the effulgent form of the Ishta Devata or the tutelary deity.
When the mind gets highly purified, when meditation and devotion become intense and profound the mind rises to Visuddha Chakra or the centre in the throat, and experiences more and more powers and bliss. Even when the mind has reached this centre, there is a possibility for it to come down to the lower centres.
When the Yogi reaches the Ajna Chakra or the centre between the two eyebrows he attains Samadhi and realises the Supreme Self, or Brahman. There is a slight sense of separateness between the devotee and Brahman.
If he reaches the spiritual centre in the brain, the Sahasrara Chakra, the thousand-petalled lotus, the Yogi attains Nirvikalpa Samadhi or superconscious state. He becomes one with the non-dual Brahman. All sense of separateness dissolves. This is the highest plane of consciousness or supreme Asamprajnata Samadhi. Kundalini unites with Siva.
The Yogi may come down to the centre in the throat to give instructions to the students and do good to others (Lokasamgraha). -- SRI SWAMI SIVANANDA A DIVINE LIFE SOCIETY