Why do I have to take the GRE?
Many people wonder the purpose of a "useless" exam that tests high school math and their knowledge of a bunch of words that no one uses in real life. The purpose of the GRE is very simple. The GRE is a standardized test, and serves the same purpose that all standardized tests serve--to provide a means of measuring skill level.
Sure, graduate schools could hand out admissions based soley on grades, but how can they judge an "A" at a not-so-prestigious university and an "A" at a distinguished university? How can a graduate admissions committee know if the courses a student took were easy or difficult? It could be easy to earn an "A" at one place while it is extremely difficult at another. Such guaging becomes even more difficult when considering international students. Simply put, graduate admissions committees do not know the caliber of every school in the world and so need something else to help them in their decisions--the GRE.
In other words, the GRE helps gradute school admission committees be more objective with their decisions.
More GRE FAQs