The most important of the six basic principles of the Constitution is the principle of limited government. The other five principles of the Constitution are largely meant to ensure that government remains limited.
Limited government is the idea that the government cannot simply do whatever it wants. There are limitations that are placed on what the government can do so that it cannot take away the rights of the people. For example, the First Amendment explicitly prevents the government from depriving us of our freedom of speech. There are many other areas in which the government is not allowed to interfere. The point of this is to prevent the government from tyrannizing us.
All of the other basic principles of the Constitution are arguably meant to ensure that government will not be able to tyrannize us. We have popular sovereignty, which allows us to control the government so that it will not abuse us. We have separated the powers of government between the various branches and we have given them checks and balances over one another, including the power of judicial review. In addition, we have divided powers between the federal government and the state governments. All of these things are devices to make sure that no one part of the government becomes too powerful. A part of government that was too powerful could tyrannize us.
In short, the other five principles of the Constitution are all meant to strengthen the principle of limited government.