From the new afterword by the author:

Humanity has had a long fascination with blood sacrifice. In fact, it has been by no means uncommon for a child to be born into this world only to be patiently and lovingly reared by religious maniacs, who believe that the best way to keep the sun on its course or to ensure a rich harvest is to lead him by tender hand into a field or to a mountaintop and bury, butcher, or burn him alive as offering to an invisible God. The notion that Jesus Christ died for our sins and that his death constitutes a successful propitiation of a loving God is a direct and undisguised inheritance of the superstitious bloodletting that has plagued bewildered people throughout history…