How do you say Symbol in a literary sense?
basically 象征 has lots of meanings, in which you have mentioned two important. 


象征 can be used as a verb, and means symbolize or signify. In this case, 象征 uses some concrete things to describe some abstract concepts. In 白色象征纯洁, 白色 is concrete, and 纯洁 is abstract. Another example can be "白鸽象征和平" (The white dove symbolizes peace).
象征 can also be used as a noun, and means symbol. For example, 青鸟是快乐的象征 (the bluebird is the symbol of happiness). And 作者用“白色”来做象征 usually doesn't appear individually. In common cases, the writer will firstly describe something, at last he will use that sentence. For example, 她的最大特点就是纯洁,而作者用“白色”来做象征. (And here 比喻 cannot be used.)


I don't know if I have answered your question...