This section is from the book "Karpuradistotram. Karpuradi Stotra Tantrik Texts", by Arthur Avalon (Sir John Woodroffe). Also available from Amazon: The Serpent Power: The Secrets of Tantric and Shaktic Yoga.
The forms of the Mahavidya are divided into two groups namely the Kalikula and Shrikula. So Niruttara Tantra says that 'Kali, Tara, Raktakali Bhuvana, Marddinl, Triputa, Tvarita, Durga and Vidya Pratyangira belong to the Kali-kula. And to the Shrikula belong Sundari, Bhairavi, Bala, Bagala, Kamala, Dhumavati, Matanggi, Vidya Svapnavati and Mahavidya Madhu-matl. Of all the Siddhavidyas Dakshina, is, O my beloved, the Cause (Prakriti.)'
Kali-kula is for the worship of Jnanis in Divya and Virabh-ava, and Shri-kula is for the worship of Karmins in Divya, Vira and Pashu Bhavas. The Tantra Shastra gives an account of the Mantras, Yantras, mode of worship and so forth for all the ten or eighteen Mahavidyas. But almost all Tantrik writings hymn the greatness of, and give the highest place to, Kalika the first Mahavidya for the others are but different forms of Brah-. marupini Kalika. The Nigama Kalpataru says 'Of all castes the Brahmana is the highest. Amongst all Sadhakas the Shak-ta is the highest. Of Shaktas he is the chief who does Japa of the Kaltmantra.' Pichchhila Tantra also says 'of all the Mantras of the Devas that of Kalika is the best. Even the vilest can become Jivanmukta simply through this Mantra.' In Yogini Tantra, Shiva says 'This Vidya Kalika is Maha-Maha-Maha-Vidya, through whom even the worst may attain Nirvana. Even Brahma, Vishnu, and Maheshvara are Her worshippers. She who is Kail the supreme Vidya, is Tara also. The notion of a difference between them has given rise to various Mantras.' Again the Kamakhya Tantra says Oh Parameshvari, seven lakhs of Mahavidyas remain hidden. Of them all Shodashi is said to be the most sublime. But Oh Devi, the Mother of the world, Kalika is the mother even of Her.' Niruttara Tantra says ' Without knowledge of Shakti, Oh Devi, there is no Nirvana. That Shakti is Dakshina Kali who is the own form of all Vidyas (Sarvvavidyarupini).' The Yamala again says ' As is Kail so is Tara and so are Chhinna and Kulluka. Oh Devi, thou, who art the supreme Kalika, art also the Murtti which is composed of these four. In the Vaidik system Sagnika (fire-maintaining) Brahma-nas achieved their ends by the offering of oblations to the seven lolling tongues of fire named Kali, Karali, Manojava, Sulohita, Sudhumravarna, Sphulingini and Devi Vishvaruchi' (1st Saptaka, 2nd Khanda, 4th Sutra).
Another important characteristic of the Tantra Shastra remains to be mentioned. Although this Scripture is very liberal in matters of practice and worship and does not recognize distinctions of caste and so forth, it has yet repeatedly enjoined Sadhakas to keep this Achara hidden from ignorant Pashus. Of Kaulas it says that 'they are at heart Shaktas, outwardly Shaivas, and in gatherings Vaishnavas'. It also contains injunctions such as that the teaching should be kept as secret as one would the knowledge of one's mother's illicit love, and that if it is given out the Sadhaka's purpose is frustrated and so forth. In the Gandharva Tantra, Shiva says that only such men as are without dualism, have controlled their passions and are devoted to Brahman are entitled to this Shastra. ' He alone is entitled, who is a believer, pure, self-controlled, without dualism who lives in Brahman, speaks of Brahman, is devoted to Brahman, takes refuge in Brahman, who is free from all feeling of enmity against others, and who is ever engaged in doing good to all beings. Others are not true Sadhakas (Bhramasadhaka). It should not be told to Pashus, to those who are insincere, or to men of shallow knowledge.' For this reason Shiva has used symbols in the teaching of all Dhyanas, Mantras, Yantras, and modes of Sadhana of Devas and Devis. The meaning of these symbols is not known to any but the Sadguru. Hence the secret mysteries are unintelligible even to the learned without the grace of the Guru. In the Kularnava Tantra, Shiva says ' There are many Gurus who know the Veda the Shastras and so forth. But, Oh Devi, rare is the Guru who knows the meaning of the supreme Tattva '. Hence in order to know the true meaning of the Dhyanas and so forth, there is no other means than to seek refuge with the Guru who knows the meaning of all Agamas.
It is owing to ignorance of the true nature of Devata that even Brahmavidya, who is subtler than the most subtle and Consciousness Itself, seems to be a gross thing. Even learned men do not shrink from saying that this Brahmamayi, whose desires are fully realized (Purnakama) is fond of offerings of blood, flesh and so forth. In the Jnanasangkalini Tantra, Shiva says, 'Agni is the Deva of the twice born. The Devata of Munis is in their hearts. Men of small intelligence worship images. To the wise, Devata is everywhere.' That is Karmin Brahnianas worship Agni as Ishvara, Yogis see the Devata in their own hearts, men of small intelligence (that is compared with the others) worship the Devata in images, and high-souled seers of the Tattva see Brahman everywhere. In fact much as a teacher shows his little students, small globes and maps, in order to make them understand the nature of the great earth, so Gurus counsel Sadhakas of no great intelligence and of inferior Adhikara to meditate on Sthula forms in images and pictures so that their wandering minds may be rested, and they may learn the true aspects of Devata. infortunately however, ignorant men consider the Sthula form to be the true aspect of the Devata. In the Kular-nava Tantra, Shiva says that some meditate on the Sthula to still the mind, which, when so stilled, can fix itself on the Sukahma. The Sadhaka should first learn from the Guru what quality or action each limb of the image represents, and should then practise meditation on the subtle, otherwise the gross form will itself become for him mere earth or stone. In Kubjika Tantra, Shiva says ' Oh Lady of Mahesha, One should meditate on the Formless (here used in the sense as opposed to forms of images, etc.) along with the form. It is by constant practice, Oh Devi, that one realizes the formless.'