I realized after listening to Scott Powell's interview about history that my own definition of history was buried on this site. Definitions are vital because they delimit one's study and serve the need for clarity.
History is the study of the human past with the end of understanding the present.
It occurred to me, upon reflection, that I should perhaps append "and future" to the definition. This is basically what Powell suggests the purpose of history is—to "instruction, inspiration, and insight." But I'm not so sure.
History, per se, doesn't offer guidance about how to live, how to effect cultural change, or how to organize society. Those are the province of philosophy. History as a subject amasses data about the course of humanity. History as a discipline creates the tools for inferring what has transpired from what is available to us now.
This knowing where we are and how we got there is vital. History provides the context of the present. To expect of it the task of philosophy is misguided; history is the fodder—a broad, wide-ranging set of concretes—that allows us to induce philosophic principles.
That being said, the purpose of any particular person for studying history should be exactly what Powell indicated. However, historians should not do that work for their readers: they should focus on accurately laying out the facts with minimal interpretation and instruction. Otherwise historical accounts become mere pabulum like Howard Zinn's A People's History of the United States.