Taiji was "created" or evolved as a martial art. There are some reasonable indications that it evolved from a precursor style in Shanxi Province which was transplanted to Henan Province by the Chen Family, who developed the art to the current Chen style (the other styles all derive from the Chen style, to one degree or another).
Fighting was very important in the early days; it was a necessary skill. The idea that the movements, tactics, etc., conformed with the universal cosmology is an idea that is common in Asian martial arts. "Moving 'naturally'", "not resisting", etc., etc., are common ideas that come from this cosmology and those explanations are pretty common. "In accordance with the Tao" is another way of saying sort of the same thing. In other words, people seem to take philosophical and behavioral implications from what were essentially more physical and cosmological tenets. I.e, some of the understandings of Taiji and other arts that are out there are stem from wrongly approriated comments about the cosmology.
There are adjunct concepts of Wu de, "martial virtue", that are somewhat in line with some of the Taoist stuff, but that shouldn't be confused as being the innate philosophy of the martial art. Chen's taiji has the idea that a truly skilled expert can respond to an attack with a massive strike (the "hard" response) or can simply choose to handle the opponent with a throw or a lock (the "soft" response). Because of the "balanced yin and yang" tenet, Taiji is supposed to be able to do either the hard or the soft.
Back to work.