This question which Smith posits at the very beginning of his book and then sets out to answer is well addressed throughout this refutation of theistic belief which Smith has divided into four principle parts.
In Part 1, Smith attacks the general concept of God as an omniscient, omnipotent, omnibenevolent, infallible, and supernatural being. He explains the meaning of such terms as theist, agnostic, and atheist, and the implications of being each. In drawing excerpts from the writings of many theistic authors, he shows the notion of a god to be internally inconsistent and rationally unintelligible, and because theism cannot seek rational justification, he thus sets up his attack on faith.
The efficacy of faith as a means to acquire knowledge is discussed in Part 2. Faith, the shortcut to knowledge, is shown here to be inconsistent with reason in that faith calls for an abandonment of rational thought processes in favor of acceptance of an idea without empirical evidence. If faith is to be epistemologically inconsistent with reason, Smith argues, it must be shown to be valid through reason. Smith exposes the inherent incosistency between miracles and causality, and goes on to reveal contradictions within the Bible, thus forcing the Christian to relinquish his idea of the Bible as the absolute truth of God. By showing faith to be illogical and irrational, Smith cuts the ground under from the acceptance of many religious doctrines and the belief in a god.
Part 3 is dedicated to the refutation of the arguments put forth by theists for a god's existence. Each argument is presented and then addressed, and these various "proofs" offered by theists are shown to be fallacious and philosophically invalid.
In Part 4, Smith demonstrates that the Christian basis for morals is misfounded. His chapter on "rational ethics," which counters Christianity's moral basis, seeks justification for a moral system and shows that virtues which are beneficent to man are those that should be followed. Smith discusses the terrible psychological consequences of the Christian moral system and how, rather than helping man in achieving happiness, it helps to perpetuate misery. He quotes multiple passages from the Bible and shows their underlying, implicit statements. Smith concludes, "Human misery is a sad spectacle. But it is sadder still when disguised as moral righteousness."
This is an excellent exposition to atheism and is highly recommended for both theists and atheists. It is specifically designed for the layman of philosophy.
As your exposition to philosophy becomes greater, though, you will progress beyond this book, so to speak. It is a wonderful starting point, nevertheless. Additionally, for a more eclectic look at ethics, I suggest reading Nietzsche as well as several of the Socratic dialogues, specifically Protagoras and Meno.
You will not go wrong buying this book.
