The functions of constitution:
Organize the State structure: For example, in the USA, the Federal Government is divided in to three branches by the Constitution: Legislative, Executive and Judicial. The reason for this separation is to ensure that balance the power and there is no branch which controls too much
Limit the power: In the USA, Constitution limit the power of government by divide it between the national government and state government because when if not limit the power, a buse of power will appear . Although the federal government has much power over the state, all their power is limited in Constitution. And the local laws that conflict with the
Constitution or federal statutory law are barn.
Protect citizens: It means that the Constitution protect the citizen’s personal liberty from intrusions of the government .It not only protect the people live in country, it also protect live abroad and need to be protected
State need a constitution because: The constitution is basic law and the state use the Constitution to make the law more detail in specific case and help the state solve internal afraid and external afraid. Besides that, the Constitution empower the government of State
2. Some countries change their constitutions all the time, the others keep they unchanged.
Constitution is a set of fundamental rules, regulates vital subject – matters of a country. Constitution includes defining of political, economic, cultural, social regime, national defense, diplomatic policies; recognition and acknowledgement fundamental rights and duties of the citizen and other people; setting principles for establishment and operation of state organs system. Constitution is the highest effective document, the most important law of the country, fundamental and abstract provisions. When political institutions, economic – social conditions of the country change, requires creating a new institution or legislating beyond the limited terms of the current Constitution or improving the country basically, comprehensively or changing the nature of the old Constitution to respond to development requirements of the country and needs of the people in that country. The country must amend, implement or promulgate the new Constitution to create constitutional basis for the completion of the legal system.
Besides, the other countries keep Constitution they unchanged because the current constitution is in line with the current situation of the country. So they unchanged.