Here's why:
* It names a thing: Context refers to the circumstances that form the setting for an event, statement, or idea, and in which it can be fully understood.
* It can be the subject of a sentence: "The context of the meeting was crucial to understanding the decision."
* It can be the object of a verb: "We need to consider the context before making a judgment."
While "context" can be used in other parts of speech, its most common and fundamental use is as a noun.