what's the purpose of reflecting something that's happening in society in art? What does it accomplish?

Answer 1

It can reach the minds and emotions of people better than printed reports can.

Visual Arts Purpose and Overview

Purpose of Visual Arts. The K-12 visual arts program in the public schools: ... assessment includes describing, analyzing, interpreting, judging and reflecting. ... in every society as the desire to acquire a system of spoken symbols. ...
http://www.dpi.state.nc.us/curriculum/artsed/scos/visualarts/index

The Evolution of Art
In traditional societies even today, the primary purpose of art is religious or ... However, throughout the course of history as society has changed, ...
http://char.txa.cornell.edu/art/introart.htm

Answer 2

It adds a different perspective.

Have you ever seen the Editorial cartoons in a Newspaper?

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Answer 3

Art talks to the imagination, the senses, the inner person. It lets you make personal associations that words may not trigger. Words have a tendency to become "noise", and often bend the "truth".