The purpose was for Hammurab to set down a reasonable and unchanging set of laws that addressed common problems in his kingdom. The code was especially important because, up until that time in history, there really were not any wide-spread laws that unified such a large group of people.
Hammurabi wrote his code of law to establish rules of government. He tried to make it fair for everybody. For example both the accused and the accuser could provide evidence, and it is the first known law that established a presumption of innocence.
