Chesterton has taken up a tremendous task with this book and spectacularly accomplished his goals. Here, he sets out to explore and explain the nature and history of man in relation to the central event in the history of the species: the Incarnation of God as man in the Person of Jesus Christ. To accomplish this goal, Chesterton begins with the beginning of man in prehistory and proceeds through to the rise of Christianity. His goal along the way is to demonstrate the singular uniqueness of man among the animals coupled with his simultaneously insufficiency in the accomplishment of his own salvation.
The points that he demonstrates along the way include the great difference even the most primitive of man shows when compared with any of even the highest members of the animal world; the preparation for the Gospel that took place in the religious thought of the Jews, the philosophy of the Greeks, and the military and political domination of the Romans over the Mediterranean world; and the essential difference between Christ and all other teachers and religious figures the world has ever seen. And all of this Chesterton argues with his characteristic wit and wisdom, stringing together his paragraphs and chapters out of aphorisms rather than sentences in the dry, academic sense that word has taken on.
This book is a book that will have one of two effects upon the sensitive reader: it will either lead him to a conversion (or to a deepening of faith, should he already be so convinced) or it will lead him to irrevocably harden his heart against ever converting to Christianity. Either way, it is a book that will have a permanent effect on those who read it well. And that is indeed the mark of a great book.