i'm new to the forum, but since sanchin is a big part about what i am writing my thesis on, i thought i'd throw in my 2 cents for you.
Sanchin translates as "Three Conflicts," "Three Battles," or "Three Gods;" the three conflicts referring to mind, body, and spirit. Sanchin brings these three together to create a state of enlightenment. Sanchin is a widely practiced kata, present with minor variants in Isshinryu, Goju-Ryu, Uechi-Ryu, Shito-Ryu, and Shotokan.
Its origin can be traced to the stationary breathing exercises performed by Buddhist monks at the original Shaolin Monastery. These breathing exercises were developed by Bodhidharma [buddha]to provide a regimen for the monks so that they would not fall asleep during long hours of meditation. These basic exercises were then expanded by the monks into a method of empty-hand combat so they could defend themselves and their monastery from invaders.
All movements are conducted in an isometric fashion with the emphasis given in strong ibuki breathing. During sanchin, the karateka uses the breath of the han. the breath of the han comes from the diaphragm and is used for power or tension movements as opposed the the breath of the su, which are used for taeszu or speed movements.
in shorei-ryu [cousin of shotokan] we perform sanchin with open hand movements to allow the flow of chi, unlike the closed fist used in goju.
this is an aesthetic kata using isometrics to strengthen mind body and spirit. you cannot achieve satori without knowing sanchin.
if i didn't answer what you were looking for, feel free to send me a pm, and i'll try to be more specific to your thoughts.
sensei jon, 6th dan shorei-ryu