This is in fact the test and use of a man’s education, that he finds pleasure in the exercise of his mind.

Jacques Barzun (1907-2012) French-American historian, educator, polymath

Essay (1950-10-15), “The Educated Man,” Life Magazine
    (Source)

More commonly given as "The test and use of a man's education is that he finds pleasure in the exercise of his mind."

Essay collected, under the same name, in Barzun, Begin Here: The Forgotten Conditions of Teaching and Learning, ch. 15 (1991).