The rest of that quote is “the point is to change it.” Marx was a philosopher of history and the forces that change motivate historical shifts. His philosophies of historical materialism and dialectical materialism illustrate how class structures and economics largely comprise the actual physical doings of life; what he would call the Base. The Superstructure are the thoughts, ideas, religion, politics, etc. that arise from the way we go through life. If philosophers have so far only ‘interpreted the world’ the implication is that their interpretations are rarely practical or practicable; this conjures the stereotypical philosopher who sits solitary and just asks “why?” about everything. Marx was all about actually changing not just the way we think about things but the actual ways we function in daily life and that includes everything from economics to social interaction. In fact, he would say that the only way to change the way we think about things is to FIRST change the way we do things. So, his philosophy was about changing actual living conditions en route to changing how we interpret the world. Literature is a material production which has ideological power. If the point of the world is to change the actual function, then it would stand to reason that Marx would encourage literature, as a produced commodity, to be a part of that change.
This literature would certainly promote social awareness and socialist qualities of living such as sharing wealth/profit. But more to the heart of Marx’s thought, this literature would be affordable to everyone; certainly those who make it. The literature itself would include an awareness of history and the social forces that govern daily life. This is not to say that all literature in a Marxist state would have to be socialist propaganda. But that general awareness of social and historical forces would certainly have a larger role in certain genres of literature. The actual production, business of literature would also have to adhere to this ‘changing the world – not just changing the way we think about the world” ethos. So, in the literature business, there would be no corrupt CEO’s, agents, etc. Authors and publishing companies would probably have a more communal, profit-sharing structure. Remember that, for Marx, the way we do things is the only way to change how we think about things. So, with regards to literature, even the physical and socioeconomics of the production itself, would have to change; not just the content. This may sound like a drastic, dialectical way of going about things, but for a simple example, consider an author under Capitalism and an author under Marxism. One under Capitalism may be motivated by notoriety, profit and self-interest; and there is productive value and healthy competition in all that, but downsides. One under Marxism may be motivated by historical consciousness, profit as a means of making a living and social as well as self interest. Both systems seem to be direct opposites but it’s not quite that simple. Both systems have pros and cons.
But getting back to your point, for Marxist literature itself: its content and its actual production would adhere to social change in democratizing the means of production (spreading the wealth) and that philosophy about interpreting the world would change following this change in content and method/motivations of actual production of literature and every other commodity.