A constitution is a description of the institutions and rules whereby people agree to be governed. However, a document entitled Constitution says very little about its effect on the welfare and liberties of its people. Some of the most oppressive governments and poorest countries have had a "constitution". Americans have been more fortunate.
The U.S. Constitution governs through four main principles: Schechter 266-276
1. Federalism - the sharing of power between state governments and the federal government;
2. A republic - accountability to the people via its representatives, who are subject to removal from office by the people;
3. Separation of powers - power distributed among the three main branches of government - legislative, executive, and judicial;
4. Checks and balances. - power of any one branch limited by the power of the other two.
The Constitution was designed to give substantial power to the Federal Government, but this power was restricted by disseminating it among three government branches. Other restrictions gave the states limited powers and the people ultimate power through "popular sovereignty". People (meaning, voters) have the ultimate power to change the government.
More important than the document itself were the lengthy and complex web of laws, judicial interpretations, and amendments that were superimposed on the Constitution to keep the above governing principles operational without bloody revolutions, except for the Civil War between 1861 and 1865.
The Constitution, and its interpretation and execution, created a government that, together with a country rich in natural resources, a capitalist economic system, and a culture that promotes the use of technology and science, resulted in high living standards and substantial liberties among Americans.