Art the imitation

When talking about Art in the form generally described in the 17th century we are referring to imitation art, or something that is meant to appear like something that is real even though it isn't.  This brings up the debate as to the purpose of art itself.  If art is just an imitation then why do we need art and not the real thing?  What is the significance of even having art if it is just an imitation of something that we can have in real life like a chair?  Whats the point of having a painting of a chair instead of the actual chair?