There's a tradition within Reformed Christianity called presuppositional apologetics, which is essentially a system for defending the Christian faith based on the idea that our inmost assumptions about life, God and everything form a worldview that informs both our beliefs and our actions. Francis Schaeffer was a well-known apologist in this tradition, and How Should We Then Live? echoes the thought, study, and evangelism of a a very full lifetime.
This isn't an apologetics manual, a philosophy course, or anything as narrowly focused and bland as that. How Should We Then Live? tells the story of Western civilization from its Roman beginnings to the later part of the 20th century, putting everything in the context of the ideas and attitudes that guided men in each period. In this sense, the book is a Christian philosophy of history; but it's also art analysis, history proper, a defense of Christian faith and reason, and many more things besides.
While some would call Francis Schaeffer a popularizer of presuppositionalism, don't let that fool you: though his books are often fascinating or even fun to read, they aren't easy. This volume in particular seeks to cram in less than 300 pages many of the ideas he'd spent whole volumes talking about elsewhere: the Western embrace and later rejection of reason; the humanism that dogs our contemporary culture; the search for and reality of "true truth"; and many more.
The first half of the book is dedicated to the history of ideas from the days of Imperial Rome up through the rise of modern science. The second half deals with how this historical trajectory has impacted our own social context, the current status of thought, religion and science, and what Christians should expect in the future. Schaeffer's conclusions are easy to follow, since he's already laid the whole historical foundation in the beginning of the text.
Much of his analysis centers around how Western thought structures have influenced the arts. How Should We Then Live? is full of black and white images of famous works of art, from Greco-Roman statuary to Ingmar Bergman movie posters. Because some of the material is fairly explicit (and because this is sometimes a difficult text to grapple with!), this isn't a book you'll want to just hand your kids, especially kids on the cusp of adolescence.
It is a book families should become familiar with together, however. Schaeffer's analysis is alarmingly astute, and almost forty years after the book's initial publication we can see his predictions coming to fruition. This is a much-needed commentary in that Schaeffer was able to see past symptoms (the rise of evolutionary theory, the embrace of sexual liberation, etc.) to their sources in fundamentally anti-Christian ideas.
Easily one of the most important Christian books of the last century, How Should We Then Live? is more pertinent than ever. It's important to note, however, that it isn't Schaeffer's vast knowledge about (apparently) everything, his ability as a philosopher, or anything else that make his observations ultimately worth listening to. At the end, his clearly evident love of Jesus Christ and godly character are his most worthy credentials, both to other Christians and to the secular world.