Every human possesses three forms : Physical, Subtle and Causal. Physical is our gross body through which our karma (more on this here) manifests its game in present lifetime. Our Subtle represents emotions and attachments needing multiple lifetimes to untangle them so we can progress spiritually, a.k.a Atma or Soul. Our Causal form is a shard of Paramatma/Universal-being connecting us to this whole creation. This is what Upanishadic maha vakyas like Aham Brahmasmi, Sat chit ekam Brahma refers to. Once our karma gets exhausted completely and nothing remains to be desired in this world, Physical body merges into Subtle and subtle back into its origin, the Causal body.
Similarly, even Gods and Goddesses are said to possess these three forms. An effective sadhana propiates a Diety in all their 3 levels of existence. Tantra (i.e puja, homa, aarti, bhajans, nritya etc) takes aid of a Pictorial or Sculptural representation to worship a Devata’s physical form. Our mind can also easily relate to a Being , whether human or divine, if it has a name and form. Mantra is their subtle form represented through sound vibrations. Yantra is their causal form represented using abstract geometrical representations. Many Saints and Rishis experience seeing a triangle in their deep meditative states through which all beings are born; this is often referred to as Hiranya garbha or Vishwa garbha, meaning womb of this Creation denoting the Shakti principle.
If you notice top section of Gurukula.org home page, it has all these three- Lalitambika’s sublime form, Sri Yantra in her background and sound waves denoting her mantra.
It would be ideal to include these holy triad of Tantra, Mantra and Yantra in our spritual practices. Archana we do during Lalita Sahasranamam parayana is tantra, each of 1000 names of Lalitambika is her mantra and Sri Chakra her yantra. Some Vastu experts also recommend Sri yantra to remove Vastu dosha in a house. Sri Meru is a 3d representation of Sri Chakra. Note that word Sri Yantra is general term that can denote either Sri Chakra or Sri Meru (more on this here).
Its sufficient to get a 2-dimensional Sri Chakra initially for Lalita Sahasranamam and Khadgamala stotram and get Sri Meru after learning Sri Yantra puja viddhi which comes much later during Lalita upasana charana.
Sri Matre namah
Thank you for this information. Some of my questions were answered in the writeup.