The Bible teaches us that government is a God-ordained institution whose core purpose is to restrain evil, promote good, uphold justice and righteousness, and provide peace and order. As citizens, we should submit to government authority unless it contradicts the Word of God. This is because God ultimately rules over all governments.

"Everyone must submit to governing authorities. For all authority comes from God, and those in positions of authority have been placed there by God. So anyone who rebels against authority is rebelling against what God has instituted, and they will be punished. For the authorities do not strike fear in people who are doing right, but in those who are doing wrong. Would you like to live without fear of the authorities? Do what is right, and they will honor you. The authorities are God’s servants, sent for your good. But if you are doing wrong, of course you should be afraid, for they have the power to punish you. They are God’s servants, sent for the very purpose of punishing those who do what is wrong. So you must submit to them, not only to avoid punishment, but also to keep a clear conscience."
~ Romans 13:1-5 NLT

"For a child is born to us, a son is given to us. The government will rest on His shoulders. And He will be called: Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace."
~ Isaiah 9:6 NLT

The United States of America is a soverign nation founded on Christian Principles as found in the Word of God. Our Founding Fathers looked to God's Word to inspire the tenants of our Constitution as a covenant across generations. The U.S. Constitution defines the role of government through its Preamble and the structure laid out in Articles I–VII. 

The Preamble of the U.S. Constitution

"We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defense, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America."

In short, the Constitution creates a federal government whose purpose is to form a unified nation, establish justice, maintain peace, defend the country, promote general welfare, and secure liberty for both the present and future generations.