What is the meaning of Marx's statement "Philosophers have so far interpreted the world. The point, however, is to change it" regarding literature?
The point of Marx's Theses on Feuerbach is to attack the divide between the contemplative and the active in philosophy. Philosophy had privileged the contemplative since the time of the Greek philosophers Socrates and Plato, who believed that the ideal world of the mind was superior to the imperfect and, to them, shadowy material world.
In Theses on Feuerbach, Marx sets the idea of the superiority of the contemplative over the active on its head. To Marx, the value of philosophy comes in "praxis," or putting philosophical ideas into practical use. Marx did not want to simply talk about changing the political and economic systems, he wanted to do it, which is the message conveyed in the quote cited about changing the world.
A Marxist theory of literature, therefore, would model the change in the world in a way such that people could enact—or be—this change. It would help birth the new world order by showing people what it looked like. This is why Marxist literature often depicted the worker in a bold and idealized manner.
The full statement reads: "The philosophers have only interpreted the world, in various ways. The point, however, is to change it." It comes from Marx's 1845 paper "Theses on Feuerbach." The meaning of the statement in literary terms is that most writing in Marx's time tended to repeat the philosophical ideas that came before it; because people tend to agree with their favorite authors, the philosophies used in writing almost always agreed with the original interpretations of philosophers. Because of this, the world rarely changed in any substantial way. Marx believed that writing, both in philosophy and other areas, should present new ideas and new ideals that can be studied and adopted. This would result in substantive changes to the world, and increase the likelihood of Marx's own philosophies being adopted at a wider level.