When people enter into society, they forfeit some of their natural rights and promise to abide by common laws that are based upon their common understanding. The purpose of this is to protect life, liberty and property of people. People give some of their natural rights to society and society in turn hand that to government. So the purpose of government is to ensure rights of people.
As time elapses, everything changes and so are people’ desire and need, hence people’ representatives have to pass new laws that represent per people’ need, and debate on necessity of old laws on regular basis. Whenever that democratic process is abrupt, then there is no meaning of that legislature. When a legislative body has no longer power to assemble to discuss the contemporary political issues and people’ will, then that legislative is not legitimate as it doesn’t represent contemporary will of people and guarantee civil rights. (Current interim parliament is not as per people’ will so it is not valid)
The law that protect people’ natural rights in society can be justifiably enforced only by those who are true representatives of people. That means, the representatives that govern legislative must be chosen directly (Constituent assembly). Then only people can be sure that the representatives will represent their will and protect their rights (It did not happen in 2007 and 2046 so called revolutions). For instance, if a prince changes way the election is held and ensures that only his followers be elected, then those who are elected will serve for the prince not for people. The pro prince representatives will alter everything in government to meet their interest ( It happened in the panchayat system and still we can not rule it’s possibility because most of high ranks army officials are still core royalists).
A king has army, property and followers. He can use all of his powers to subordinate people and their rights. If a king no longer abides by people’ will and enforces his own will as the state’s law then there is a state of tyranny. Rebellion is the only way to take people’ rights back ( gyanendra did that and Nepali people rebel).
The executive body of government is the one that make sure everybody in society follows law. Law is not made for itself; it is passed so that it can be executed properly to place everything in order and just manner. When executives do not perform their duty or abuse their rights for their own sakes, then that will make society anarchy, where everyone does whatever they want without obeying any law or order(parties have always done this).
When the government try to enforce its arbitrary will, when it hinders assembly of people’ representatives, when it changes the way election is held, when people rebel and when laws approved by people are not enforced properly, then that government should be dissolved. After dissolution of such government, people can use their own natural rights to replace the old one with new one that will represent their will and guarantee their rights of life, liberty and property. Constituent assembly is must
Source: Two treatises of government, John Locke