we are told about the lottery, but not its exact purpose. Do the towns people know? Is this omission significant? Intentional?

The only clue we are given about the origins of the lottery is vague at best. Old Man Warner complains that the lottery is not like it used to be. He says, "lottery in June, corn be heavy soon." This speaks to some sort of sacrifice for the crops to be healthy. I think the reasons behind keeping the reasons vague is to add to the irony of the situation. These village people really have no idea why they are killing someone.