Could both atheists and fundies answer a modest question?

Why is it, when I read, say, Sam Harris's "Letter to a Christian Nation," it all makes perfect since, it is of, by, and for the 21st cenury, but when reading the OT I confront a talking snake, genocide, the of virgins, human sacrifice, slaughter of innocent children, , slavery, stoning to death a child who ses, a woman born from a man's rib, a flat earth, trillions of galaxies in each of which there are trillions of stars created as an afterthought, and so on and on and on? And presumably educated adults dismiss the first and swear up-and-down that they believe in the second.