A cognitive semiotics of Western Esotericism is proposed with reference to the opaque aspects of esoteric discourse and texts, exemplified by Crowley's Liber AL and the tradition of Thelema. Such discursive opacity (leading to failed interpretation) is a semiotic problem, as it would hardly be tolerated in ordinary communication due to expectations of relevance (i.e. that the discourse will be intelligible and informative). It is argued that this is different when the context is religious, i.e. that in religious contexts, opaque signs/texts will effect a shift in interpretive strategy from linguistic interpretation (to understand the text’s linguistic import) to indexical interpretation (intuitions about the text’s background), leading to a psychological effect, a motivating sense of relevance—the relevant index effect. Findings in the cognitive study of reading provide suggestive evidence in this vein. With reference to the relevant index effect, a model for the transmission of esoteric traditions is proposed. In conclusion, theoretical and empirical avenues are explored.