While technically the preamble is viewed as the introduction, it is actually the contractual agreement between the People and the Federal government.
THE PEOPLE create an entity, the Federal Government, with goals and it is done through the following instrument, framework to achieve those goals. If there is no contract, the Constitution becomes a meaningless piece of parchment and the de facto government has no obligation to do anything, and can very well act to enslave the very people who created the government.
