To understand many things in Hinduism and the symbolism we should try to understand how this universe was born and came to existanse , and we as human being are made by the God . Adi Shankaracharya had written this in two books called Atmabodh and Tatwabodh..
So let me state as I understand. There 3 bodies , one causal, one astral, one physical . As the neme imolies the causal boby is the cause of rest of them. The astral body is behind the physical body and causal body acts through astral body and the impressions are stored in to it . No need to explain physical , though it will need to be when we will talk about it.
There are 3 ' Gunas ' or the qualities', Satwik ',' Rajasik' and' Tamasik.'