Audre Lorde, the American poet and essayist. The sentence is in A Burst of Light (Firebrand Books, 1988), in the essay “A Burst of Light: Living with Cancer”. Wikiquote gives it with page 125 and the sentences around it. The full sentence ends “and that is an act of political warfare”, which is usually cut.
What it means
Looking after your own health and strength is not a luxury but a way of surviving, and for someone whom the world does not expect or want to survive, survival is itself a form of resistance.
Where it comes from
The line sits in a passage about her own limits. As Wikiquote gives it, the sentences just before it are: “Overextending myself is not stretching myself. I had to accept how difficult it is to monitor the difference. Necessary for me as cutting down on sugar. Crucial. Physically. Psychically.” Then: “Caring for myself is not self-indulgence, it is self-preservation, and that is an act of political warfare.”
Wikiquote describes Lorde as a Black writer, feminist, womanist, lesbian and civil rights activist. The essay, subtitled “Living with Cancer”, is about staying alive and working while ill. In recent years the first half of the sentence has been widely used to justify self-care in general, sometimes without the second half, which is what gives it its edge. The meaning here is offered as a reading of the passage, not as advice.