Answer:
A constitution has been regarded to be the main law of land. The reason is that it is the God father of all laws in India. To be precise, it contains all laws mentioned in a clear cut manner. As it is the creator of all laws, it has been regarded to be the main law of land
In general a constitution is the charter of a government that sets form of government, the general organization of the government, the basic national law of the land, the legal authorities of the various departments, the limits on the government, and the rights of the citizens. It is the legal framework to which all lower laws must comply. So it is the base, overriding law, or as you say, the main law.
The US Constitution does this as well, and since the country was formed from a group of independent states, it specifically names the power given by the states to the federal government and says that any thing that is not specifically given to the federal government rightly remains with the states. That is why in the US some states have very different laws from other states. As long as state laws do not violate federal law they have a right to do things the way they see fit. But, for instance, since the Constitution has banned slavery, no state can declare it illegal. Any federal law that does not conflict with the Constitution supersedes any law of a state. By the same token any federal law that conflicts with a Constitutionally protected state law, would cause the Supreme Court to invalidate the federal law. The Constitution is the supreme law of the United States.
