The answer is :
Since changing the Constitution, which is the foundation for all other laws in the country, is very difficult therefore; it is not easy to make consitutional amendments. Furthermore there is always a procedure for determining whether new laws are anti-constitutional for this there is a special procedure where only the jurists responsible for this meet and discuss the availability of introducing new laws or seeking amendments. The method for modifying is typically written into every constitution. The procedure varies depending the country but in general a special procedure is always required.
In the case of the Constitution of the United States of America ,the Constitution provides that an amendment may be proposed only either by the Congress with a two-thirds majority in both the House of Representatives and the Senate or in the presence of a constitutional convention called for by two-thirds of the State legislatures.