"We the People…"
The first and most basic principle of the Constitution—the principle of limited government—begins to emerge in the very first three words of the Preamble. The government of the United States, those three words declare, only exists because We the People choose that it should exist.
Thus the government has no natural or God-given powers; it has only whatever limited powers we choose to give it. The government is not all-powerful. It has no right to try to do more than we've explicitly authorized it to do. It is limited.
The idea of limited government pervades the entire Constitution. Huge sections of the document include long lists of things that the government cannot do. Just look at the first words of the First Amendment, which guarantees cherished rights to freedom of speech, religion, the press, and assembly: "Congress shall make no law…"
The principle of limited government expands upon the idea of popular sovereignty (the idea that legitimate political power must derive from the consent of the governed). If the people are the only real source of the government's authority, then the government naturally should have only whatever limited authority the people want it to have. The Constitution is the place where we state, clearly and explicitly, which powers we choose to give to the government and which powers we refuse to give to it.