In one of the Transcendentalist Ralph Waldo Emerson's essays, Education, he wrote of his philosophy of life, whose basis was the inner resources of the self and revelation from the divine presence of the soul. Among the factors that Emerson felt worked against these resources of the self was what he termed "the opium of custom." This phrase has a direct corollary to Shirley Jackson's short story "The Lottery." For, its theme can be stated using this very phrase: Jackson's short story demonstrates the evil of "the opium of custom."
Because the lottery is a custom of the village, some people follow this custom unthinkingly, and they even go so far as to praise it. It is held because, as Mr. Warner says, doing away with it would only cause trouble. He snorts at any change,
"It's not the way it used to be....people ain't the way they used to be."
The lottery is also held with Mr. Summers in charge because he "has the time and energy to devote to civic activities." And, there is a sense of the importance of continuing these activities. Mr. Summers, who "waits with an expression of polite interest" until a villager finishes talking so he can say, "All right, folks,...Let's finish quickly." Mr. Summers simply wants to finish so he can return to his regular routine. Clearly, here, the citizens have become inured to the senseless and random cruelty of the lottery. Indeed, they are drugged by "the opium of custom."
Mr. Warner also says "Used to be a saying 'Lottery in June, corn be heavy soon.'" The theme of The Lottery is the mindless leming-like following of customs/traditions without questioning the purpose.