Kundalini is the Sanskrit name for the fire of the pentecost that empowers and awakens the apostles; it is the serpent raised by Moses. Kundalini is the energetic basis of becoming an angel, buddha, master, etc.
"Kundalini is the cosmic power in individual bodies. It is not a material force like electricity, magnetism, centripetal or centrifugal force. It is a spiritual potential Sakti or cosmic power. In reality it has no form." - Swami Sivananda
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Although the term Kundalini is from Sanskrit and is associated with Indian mysticism, tantra, and yoga, the word refers to a living element in nature and is thus known in all religions by different names. In Judaism and Kabbalah, it is called Shekinah. In Christianity, it is the fire of the Pentacost that illuminated the apostles. In Buddhism it is known by many names, such as Candali.
"Kundalini, the serpent power or mystic fire, is the primordial energy or Sakti that lies dormant or sleeping in the Muladhara Chakra, the centre of the body. It is called the serpentine or annular power on account of serpentine form. It is an electric fiery occult power, the great pristine force which underlies all organic and inorganic matter. Kundalini is the cosmic power in individual bodies. It is not a material force like electricity, magnetism, centripetal or centrifugal force. It is a spiritual potential Sakti or cosmic power. In reality it has no form. [...] O Divine Mother Kundalini, the Divine Cosmic Energy that is hidden in men! Thou art Kali, Durga, Adisakti, Rajarajeswari, Tripurasundari, Maha-Lakshmi, Maha-Sarasvati! Thou hast put on all these names and forms. Thou hast manifested as Prana, electricity, force, magnetism, cohesion, gravitation in this universe. This whole universe rests in Thy bosom. Crores of salutations unto thee. O Mother of this world! Lead me on to open the Sushumna Nadi and take Thee along the Chakras to Sahasrara Chakra and to merge myself in Thee and Thy consort, Lord Siva. Kundalini Yoga is that Yoga which treats of Kundalini Sakti, the six centres of spiritual energy (Shat Chakras), the arousing of the sleeping Kundalini Sakti and its union with Lord Siva in Sahasrara Chakra, at the crown of the head. This is an exact science. This is also known as Laya Yoga. The six centres are pierced (Chakra Bheda) by the passing of Kundalini Sakti to the top of the head. "Kundala" means "coiled". Her form is like a coiled serpent. Hence the name Kundalini." - Swami Sivananda, Kundalini Yoga
The word kundalini in Sanskrit is कुण्डलिनी.
"Kundalini is a compound word: Kunda reminds us of the abominable "Kundabuffer organ," and lini is an Atlantean term meaning termination. Kundalini means "the termination of the abominable Kundabuffer organ." In this case, it is imperative not to confuse Kundalini with Kundabuffer." - Samael Aun Weor, The Great Rebellion
These two forces, one positive and ascending, and one negative and descending, are symbolized in the Bible in the Book of Numbers (the story of the Serpent of Brass).
"And the LORD sent fiery serpents among the people, and they bit the people; and much people of Israel died. Therefore the people came to Moses, and said, We have sinned, for we have spoken against the LORD, and against thee; pray unto the LORD, that he take away the serpents from us. And Moses prayed for the people. And the LORD said unto Moses, Make thee a fiery serpent, and set it upon a pole [spinal column]: and it shall come to pass, that every one that is bitten [by the descending serpent], when he looketh upon it [the ascending one], shall live. And Moses made a serpent of brass, and put it upon a pole, and it came to pass, that if a serpent had bitten any man, when he beheld the serpent of brass, he lived." - Numbers 21
There are seven serpents of kundalini, which correspond to seven "bodies."
"The first serpent belongs to the physical body; the second serpent to the Ethereal Body; the third to the Astral Body; the fourth to the Mental Body; the fifth to the Body of Willpower; the sixth to the Body of the Consciousness; the seventh to the Innermost, our real inner Being. These are the seven portals of initiation. These seven serpents rise in a successive order; these are related to the first seven great Initiations of Major Mysteries." —Samael Aun Weor
"Each body has its "cerebrospinal" nervous system, its medulla and Kundalini. Each body is a complete organism. There are, therefore, seven bodies, seven medullae and seven Kundalinis. The ascension of each of the seven Kundalinis is slow and difficult. Each canyon or vertebra represents determined occult powers and this is why the conquest of each canyon undergoes terrible tests." - Samael Aun Weor, The Zodiacal Course