Yantra in Tantra and rituals in Hinduism is a symbolic representation of a deity. The term yantra is derived from the root yam, to control. Yantra worship is an essential feature of tantrasadhana, and it is also a mystic process of awakening the divine power. When a tantric worshiper attains a higher degree of spiritual process, he is initiated into yantra worship. Yantras are symbolic representation of god/goddess in his/her different manifestations. In a tantric ritual, yantra of the main deity is always worshipped as a symbol of the God/Goddess. Every yantra is a sacred enclosure, a dwelling or receptacle of an ishta devata.
It is a substitute for an anthropomorphic image of the deity, e.g., Durga yantra is a substitute of Goddess Durga. At the time of Durga worship one is expected to worship Durga yantra for better prosperity. It is believed that in tantric worship there is a close relation between the deity and yantra. A yantra is a body and the deity is the self. It is believed that if one worships with yantra the deity is pleased. The deity in the form of mantrais ensiled by mantra, and thereby the deity is believed to be immediately satisfied if it is worshipped in yantra (yantre sa pujita devi sahasaiva prasidati – Kularnavatantra VI.85). A yantra is said to be capable of controlling all sorts of sufferings. It protects the worshiper from negative forces and other serious dangers. Shilpaprakasha (II.504) says that without offering worship to Kamakala yantra, Shakti worship and sadhana do not bear fruit. Ramapurvatapaniya Upanishad (I.13) states that the arrangement of a yantra in the body of a deity confers safety.
Yantra worship is employed to reach the four goals of human life – dharma, artha, kama and moksha. Once can fulfill any desire by worshiping yantra-devata sincerely and devotedly. But any mistake on part of the worshiper lands him in great trouble. Sometimes negligence of the esoteric rituals may lead to lunacy and even death. A guru alone can help ad guide in this intricate problem of mysticism.
Yantras are of various kinds. Saradatilaka (Chaps VII and XXIV) discusses in detail the formation and esoteric significance of different yantras – Raksha Yantra, Gayatri Yantra, Mrityunjaya Yantra, Agneya Yantra, Marana Yantra, etc. These yantras are employed for different objectives. Ahirbudhnya Samhita (Chaps XXI-XXVII) describes yantras, their respective merits and the way of meditating upon yantra-devatas. It further elaborates the procedure of the worship of Sudarshana Yantra by a king and other personages desiring prosperity.
Sri Yantra is the most celebrated of all tantric yantras. It is known as Sri Chakra, which is geometric representation of the Goddess Lalita or Tripura. In the worship of Sri Yantra, personal and impersonal aspects of Brahman are harmonized. Ritual and meditation lead to the knowledge of unity, through which on attains supreme peace and the highest bliss.
Thus, yantras restrain restless movements of mind and help one to concentrate on the diagram representing the deity to be worshiped. It is obvious that yantra (worship) may provide its worshiper better prosperity in life. A number of tantric and non-tantric texts with illustrations lay down rules, describe and illustrate the methods and other aspects of yantra worship.