It's difficult to answer your question, without having some idea of what you think the phrase currently means. But I guess that you are referring to "Context is all" from Margaret Atwood's 1986 feminist, sci-fi novel, The Handmaid's Tale, where the phrase is used in relation to the context of a leading character's [Offred's] life; though some critics also read it as referring to the context of the book itself - which is perhaps more the current sense you have in mind.