Conversation so far:
What is Canada's Geological Survey and how does it relate to Edward Sapir?
As director of the Anthropological division of the Geological Survey of Canada, Edward Sapir embarked on a project to document the Indigenous cultures and languages of Canada
Around what year was the Canadian Geological Survey which Edward Sapir embarked on?
In the years 1910–25 Edward Sapir established and directed the Anthropological Division in the Geological Survey of Canada in Ottawa.
How did the Canadian Geological Survey which Edward Sapir embarked on turn out?
Unsatisfied with efforts by amateur and governmental anthropologists, Edward Sapir worked to introduce an academic program of anthropology at one of the major universities, in order to professionalize the discipline.
Was Edward Sapir successful in introducing academic rigor to the anthropological study of indigenous Canadians?
Edward Sapir insisted that the discipline of linguistics was of integral importance for ethnographic description

Question: Why did he say that?
Self-contained rewrite: Why did Edward Sapir insist that linguistics was of integral importance for enthographic description of indigenous Canadian groups?