Marx's point is that philosophy has not been used to practical ends. Though philosophers produce abstract ideas about the world, people do not adapt these abstractions into making practical changes in the world. In other words, philosophy is entirely abstract—with little connection to one's everyday life.
If this statement were applied to literature, it would mean that writers take on the abstract elements of life rather than address the practicalities of life. The question is whether writers, rather than basing their works on abstractions or larger themes, should instead turn to addressing ways people can change reality. Good literature, it could be argued, accomplishes both these ends. It deals with the larger conditions of human existence through examining the ways people live and poses ideas about how people can change.
Marx's brief essay "Theses on Feuerbach" ends with the words:
The philosophers have only interpreted the world, in various ways; the point is to change it.
Marx's point is that ever since Plato, philosophers have written about the best way to govern a state and similar practical questions, but they have contented themselves with reaching a theoretical conclusion. Moreover, even the theoretical conclusions of such philosophers as Feuerbach are flawed because they insist on viewing "man" as an abstraction rather than as the product of a particular form of society. Marx therefore wants to correct this theoretical error with a healthy dose of praxis as succinctly as possible, writing:
All social life is essentially practical. All mysteries which lead theory to mysticism find their rational solution in human practice and in the comprehension of this practice.
This done, he ends his analysis with a remark which renders further words superfluous. Once philosophers have their theory right and are thinking in terms of changing the structure of society rather than the individual then they can begin, as Nietzsche was later to put it, "to philosophize with a hammer."
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.