It is a philosophical reflection on the real meaning of leisure, work, being human, and life. The second half of the book is another reflection on the nature of the philosophical act of the intellect as it stands in awe of wonder, as it really experiences reality.
The Introduction to the most recent edition is written by Roger Scruton while the original English edition's Introduction was written by T. S. Eliot.
Here is a bit from Scruton's Introduction:
"Don't just do something: stand there!" The command of an American President to a fussy official was one of those rare moments in American politics when truth prevailed over industry. Josef Pieper's serene reflections on the art of being serene ought to be read by every practical person--and the more that person is involved in business, politics, and public life, the more useful will Pieper be to him. For here, in a succinct yet learned argument, are all the reasons for thinking that the frenzied need to work, to plan, and to change things is nothing but idleness under other names--moral, intellectual, and emotional idleness. In order to defend itself from self-knowledge, this agitated idleness is busy smashing all the mirror in the house.
Leisure has had a bad press. For the puritan it is the source of vice; for the egalitarian a sign of privilege. The Marxist regards leisure as the unjust surplus, enjoyed by the few at the expense of the many. Nobody in a democracy is at ease with leisure, and almost every person, however little use he may have for his time, will say that he works hard for a living--curious expression, when the real thing to work for is dying. (xi)