Perhaps, you thought that "beauty" should be in the Accusative because the predicate is expressed by the verb in the Passive Voice "призвана". I.e. somebody views beauty as able to to save the world, so "beauty" semantically is the recipient of someone's action.

However, both It-ogo and Medved were right pointing to the fact that "красота" functions as the subject of the sentence: what is the sentence about? About "красота", therefore, it is the subject o the sentence, from the point of view of syntax.