It's a pretty sure bet that humans have been casting spells for as long as humans have existed. It is just the comparatively recent religions, including modern science, that have chosen to take a dim view of it.
Working magic was regarded first as the impious use of evil powers, and later as a deluded resort to imaginary powers. In fact, it is neither.
Magic stems from very real and morally neutral powers inherent in the human soul. We cast spells for the same reasons we use tools and language, create art and social institutions.
We are a species peculiarly prone to symbolic thought, and we are driven to exert change on the the world around us, for good or for ill. Magic is just one of many ways that those traits manifest themselves.
