In "On Cannibals," Montaigne reverses contemporary European belief in the superiority of Western culture. In many ways, his is the classic articulation of the "noble savage" trope in European literature. Far from being ignorant and barbarous, Montaigne's cannibals live in harmony with nature and have perfect, simple systems of religion and government.
These nations then seem to me to be so far barbarous, as having received but very little form and fashion from art and human invention, and consequently to be not much remote from their original simplicity. The laws of nature, however, govern them still, not as yet much vitiated with any mixture of ours: but 'tis in such purity, that I am sometimes troubled we were not sooner acquainted with these people...
The cannibals that Montaigne describes are in constant warfare with other nations, and their warriors are always brave. When they defeat an enemy, they cook an eat him, but Montaigne asks his readers to remember that in Europe, people are sometimes tortured and burned alive, and for the sake of religion, not warfare. This, he thinks, is much worse. "I conceive," he says, "that there is more barbarity in tearing a body limb from limb by racks and torments...than to roast and eat him after he is dead."
Montaigne clearly idealizes the cannibals at the expense of Europeans, whose practices he portrays as corrupt, barbaric, and brutal. He is particularly critical of the Church, contrasting it with native priests who only teach about courage and love. His point, then, is to encourage Europeans to take a critical look at their own behavior. His larger significance, however, is that he articulated an almost sociological approach to social mores. Today we would call it cultural relativism, but it was a new way of thinking in Montaigne's time. The ideas that, as he puts it, "