This is a allusion to the pagan custom of making a sacrifice to increase the harvest. Before the world's major religions began, there were many cultures that believed that some god or gods would be pleased with sacrifices and reward the people with a better harvest. In fact, there are probably still some cultures that practice this custom. Even today, many mainstream religions have rituals that are deeply rooted in the harvest, even though most of us go to the supermarket now. One holiday occurring right now in Judaism is Sukkot, which involves building a small structure with no roof, but decorated with hanging fruits and vegetables, which is meant to remind us of the small huts built in the fields as the harvest was going on. Jackson seems to be suggesting, I think, that in some ways mankind has not advanced very far beyond primitive paganism.