Barthes did not stay still. The semiological critic of bourgeois myth in 1957 became, by the late 1960s, something harder to categorize: a poststructuralist theorist of the text, a celebrant of the pleasures of reading, and eventually the elegist of his own mother's death (Camera Lucida, 1980). The evolution is not a rejection of the early work, the concern with how meaning is produced, circulated, and naturalized runs throughout, but a significant deepening and complication.
The Death of the Author (1967) is Barthes's most famous single essay, and it is best read as a direct extension of the Mythologies project. In Mythologies, Barthes showed how myth naturalizes contingent meanings by presenting them as eternal facts about the world. among the most powerful forms of naturalization in literary culture is the author as origin and authority: when we ask what a text means, we ask what the author intended. The author becomes the theological ground of the text's meaning, the Author-God who guaranteed that there was a single, stable, recoverable meaning behind the words.
Barthes's move: kill the Author-God and free the text. Once the author is no longer the privileged site of meaning, the text opens into multiplicity. Writing, Barthes argues, is not the expression of a prior subjectivity, it is an activity, a performance, a space in which multiple cultural codes intersect without any of them being primary. A text is not the linear emission of a single message from a sender (author) to a receiver (reader) but a multi-dimensional space in which a variety of writings, none of them original, blend and clash. The meaning of the text is not behind it (in the author's intention) but in front of it: it is constituted by the reader in the act of reading.
This is not license for arbitrary readings. It is a structural claim about where meaning lives in the signifying process. As the Wikipedia article on The Death of the Author notes, Barthes says writing constitutes "a multi-dimensional space, which cannot be 'deciphered', only 'disentangled.'" The liberation of the reader is simultaneously the liberation of the text from the myth of single, stable, authorially guaranteed meaning.
S/Z (1970) takes this further. Barthes analyses Balzac's short story "Sarrasine" with almost absurd closeness, 93 fragments, 561 lexias (units of reading), five codes, and in doing so establishes his most influential distinction: between the readerly (lisible) and writerly (scriptible) text. The readerly text is the comfortable, classic realist novel: it has a fixed meaning, a coherent narrative, a stable world that the reader is invited to consume passively. The reader has no work to do except receive. The writerly text. and Barthes is prescribing here as much as describing
The connection to the Mythologies project is direct. Readerly texts do for literature what myth does for culture: they naturalize a specific arrangement of meaning and social reality as the only possible one, requiring only passive consumption. Writerly texts, and writerly reading practices, resist this naturalization by requiring active, productive, creative engagement with the multiplicity of signification. The political valence of Barthes's later work is less direct than the ideological critique of Mythologies, but the underlying concern is the same: against the ideological closure of naturalized meaning, for the productive openness of genuine engagement with signs.