It beeped!

But beyond that, the point of Sputnik was to 1) beat the US at this accomplishment (this was very deliberate; the Soviets knew the US satellite-testing schedule and wanted to beat it, to show the world that the Soviets were on par with the US technologically); 2) demonstrate the capabilities of the rocket it was attached to (because this was also the same rocket as their first ICBMs — the early US and Soviet space programs were explicitly dual-use, and every accomplishment in space work was an implicit threat about nuclear capabilities); 3) part of a broader space program that worked in sequential pieces (first the beeping satellite, then a dog, then an instrumentation satellite, and so on), so that one could learn from the successes and failures that had come in each stage previously.

But don't underestimate the beep! Anyone with a radio could tune in to Sputnik's beeping, globally, as it passed overhead. It "personalized" the activity for people around the world, and made them part of it. This was an immense publicity coup for the Soviet Union — this was them saying to the world, "less than a generation ago, we were peasants; now we have atomic bombs, missiles, and satellites." It was seen by people globally as a huge deal. One of my favorite quotes-of-the-zeitgeist came from US Rep. Clare Boothe Luce, who proclaimed that those beeps were "an intercontinental outer-space raspberry to a decade of American pretensions that the American way of life was a gilt-edged guarantee of our national superiority."