The stories in this book belong to Heinlein's Future History series, and most editions of this book reproduce the two page chart of that future, detailing the social, scientific, and political changes that would happen in the next seven hundred years or so.
"Life Line" was Heinlein's first published story, and it was immediately evident that he brought a new focus to field of science fiction, for although this story has a neat gadget, a machine that can predict the exact day and hour of a person's death, all the emphasis of the story is on how such a device will impact individuals and society as a whole, rather than on the `golly gee whiz' of the device itself. Certainly not his best story, as it is too short and the characters are not fully fleshed out, but it started a revolution.
"Let There be Light" deals with two scientists who figure out a way to transform sunlight into electricity at near 100% efficiency and extremely cheaply, but who find they can't sell it due to pressure from the existing power generation companies. The two main characters are near stereotypes, and the attitude of the male towards his female counterpart may strike many as extremely chauvinistic, an attitude that was quite prevalent in Heinlein's writing from this period. But it should be kept in mind that this was the general American attitude towards women at this point in our history. Of more interest is the apparent `conspiracy' of the power companies to bury this invention. Heinlein's explanation for their actions brings this into focus as a natural reaction of companies attempting to protect their source of income - and in doing so exposes one of the real problems with unfettered capitalism.
"The Roads Must Roll" gives you get a good sense of just why Heinlein came to dominate the science fiction field so rapidly, as the story rings with real world ambience, even though the envisioned technology is one case where Heinlein got it seriously wrong, seeing giant conveyor belts, or rolling roads, as replacing the car and railroads, thus leading to a strong dependence of the economy on them. Those who keep those roads rolling are in an obvious position of power and the story is all about one such case of the `little guy' attempting to force things to go his way. The story is well told, the characters on both sides of this battle are quite believable, the social organization makes sense. Thematically, the story addresses the sense that many who work in essential industries have that THEY should be the ones who make all the decisions, who cannot see that our civilization is made of many specialties, all of whom are necessary to the continued functioning of the society as a whole. Within the confines of this story there is an encapsulation of many of the larger battles caused by this attitude, from the great owner/union fights of the early portion of twentieth century, to the more generalized battle between the ideas of socialism and capitalism.
"Blowups Happen" deals with the stresses that men come under when trying to monitor and control an atomic power plant, with the knowledge that one small error could make the whole thing blow up and wipe out at least three states, if not the whole planet. Written in 1940, before the exact details of controlled nuclear fission were known, it may seem a little dated today. But as the story is truly about how people react under this kind of extreme pressure, and what, if anything, can be done to help people cope with it, it is still a very relevant story.
"The Man Who Sold the Moon" is the longest piece here. D. D. Harriman is a man who not only has a dream of traveling to the moon, he has (almost) the financial means to do it. Harriman's schemes to not only raise the necessary money but to ensure that he will retain control of the moon once he gets there are convoluted, devious, devastatingly logical - and almost the complete antithesis of the way NASA has actually gone about it. You might think that this story is hopelessly outdated - after all, we've actually been to the moon! But the story has much to say about the world of today. Government financing of space travel will only go so far. Private financing and people figuring out how to make a profit out of this frontier will be the ultimate driver - and a very large amount of the points this story makes are very applicable to such an approach. But perhaps more important than the actual method Harriman uses to achieve his dream is the very fact that he has such a dream. Heinlein invariably presented the point that without dreamers there would be no progress, no hope for an eventual better world. Perhaps this is flaw in his writing, but I, for one, would much rather read about heroes, the dreamers, those who are attempting to change things for the better, than yet another story detailing the tribulations of a semi-neurotic Joe everyman.
"Requiem" continues the story of D. D. Harriman, now very old and in frail health, still trying to get to moon, having been prevented by his financial partners from going as too valuable to risk. This story pulls out all the emotional stops, though it is quite understated in terms of direct exposition. I have read it multiple times, and it still causes me to choke up a bit when I reach the end. It's the best story here.