His philosophy is to support or initiate a shift in literay study from work, which is the objects of literary study (novels, plays, poems, and the written word in general), to text, which is a complex of relations among readers, writers and critics as well as a complex of activities which include, reading, writing, intertextuality and production. In other words, "work" is an object or product and "text" is the production, consumption and inter-relations of that product.
This shift from work to text, comes from Marxist, Freudian and Structuralist background. The Marxist influence is the shift from product (commodity) to production (labor value, self-production). The concept of "text" is complex. From the Freudian (or Lacanian) influence, we get the "work" as that which is displayed - like a painting - and the "text" as the act of painting, relations among/between other paintings, paintings and the methodology of art. This would be the visual equivalent of intertextuality. Intertextuality is simply the relationships amongst all text, held together by metaphor, pun, metonymy, allegory, and direct reference.
Work is a thing. Text is a doing. Work is an object. Text is creating and engaging objects. So, Barthes' philosophy here, is to shift literariness from objects (in a sense, the actual books themselves) to the relations among them - intertextuality. By doing so, Barthes aims to put the production of meaning in the hands of the reader. Barthes' sees this as giving the reader an equal share with the author in producing, or interpreting, the meaning of a work. There is also an anti-patriarchal and anti-"author"-ity here. By liberating the work from the grips of the author, the reader becomes an equal participant in the process: to join the reader and writer in a single signifying process.
To sum up, Barthes aims to break away from the imposed authority of the author and to focus more on the production and relations of literature (this includes reading) instead of focusing on the objects of that production.