But when the god happens to be a deity of vegetation, there are special reasons why he should die by fire. For light and heat are necessary to vegetable growth; and, on the principle of sympathetic magic, by subjecting the personal representative of vegetation to their influence, you secure a supply of these necessaries for trees and crops. In other words, by burning the spirit of vegetation in a fire which represents the sun, you make sure that, for a time at least, vegetation shall have plenty of sun. It may be objected that, if the intention is simply to secure enough sunshine for vegetation, this end would be better attained, on the principles of sympathetic magic, by merely passing the representative of vegetation through the fire instead of burning him.
Frazer The Golden Bough.