When a writer or speaker uses asyndeton, she eliminates conjunctions like "and" or "but." This rhetorical device works to make a speech more dramatic and effective by speeding up its rhythm and pace.
Public speakers use asyndeton when they want to emphasize the gravity or drama of their topics. Abraham Lincoln used asyndeton when he talked about "a government of the people, by the people, for the people..." without including the conjunction "and." A list of items or characteristics that's not slowed down or divided by the usual conjunction feels more immediate and momentous, particularly in spoken rhetoric. In Greek, asyndeton simply means "unconnected."