This little book is a gem of its kind. It is an argument with a literal minded Christian (fundamentalist, evangelical, etc) in the form of a letter. Harris's arguments are mostly not original - some previous versions of them date back more than a century in the skeptical literature - but his concise and hard-hitting presentation of them is. He is almost unique for his honest and, one must say, sometimes blunt treatment of religion. Some readers will find this offensive and won't pay his arguments the attention they deserve. I can only ask them to persevere and see if they can find a problem with Harris's reasons. The challenge for the committed Christian is to meet him on the plane of reason; and if you think that you don't have to, because faith prevails even where reason fails, I must ask, why your faith rather than any other? As Harris points out, many Muslims have exactly as much devout belief as you do and yet you are not troubled by this; can't you see that to an outsider, this is a reason to doubt all faiths? But I am paraphrasing Harris here, and poorly. I refer you to his forceful eloquence instead.
One more thought. Where does this book leave the moderate or liberal Christian? What does it say to them? While ostensibly not aimed at them, some challenges are obvious. If you are not a literal-minded Christian, then what exactly do you believe? Why are the literal-minded Christians not just simply more consistent (less politely: less hypocritical) than you are? Are there resources within Christianity that can justify your liberal stance, or are you really compromising with outside standards and motivated by outside factors? And the final question is last, and this is treated more fully in Harris' other book, The End of Faith: to what extent are moderate religious people responsible for enabling religious extremists to thrive and thereby threaten civil society? Harris is saying that religion is false and dangerous, even in its moderate forms, and he is saying that the polite silence rational people maintain about it is morally and intellectually unconscionable. Even if you are sure that he is wrong - especially so - you owe it to yourself to read this book.