Why is power given to the Government?

Question

particularly the Australian Government

Answer 1

To provide essential services like health, education, police, defence, infrastructure (roads, power, water). Life without government is anarchic.

Answer 2

At the very least, to provide basic order and law.  Without government you have basically something resembling the Mongol horders or the Huns.  The strong rule the weak, taking what they want when they want.

Answer 3

If your country is under a government rule, all power is given to the government.