Perhaps the most overlooked announcement for the iPhone 5S was the 64-bit A7 chip, which replaces the A6 chip from the iPhone 5. While double the processing power and speed is nice, that's not exactly why the 64 bit architecture of the iPhone 5S is important. In terms of immediate effects for the iPhone 5S, all it will really do is speed up the image processing power and make more CPU-intensive functions, such as the newly announced fingerprint scanner, to occur without any serious delay.
This isn't the sole reason, however, that Apple implemented 64-bit technology. Rather, like Germany's alleged 1,000-year Reich, Apple is playing the long game, allowing up to 4GB of RAM on mobile devices. This allows Apple to release either a new Macbook or tablet with a crazy-powerful mobile processor, and eventually put the OS X on mobile devices.
While this is only speculation on the part of the tech industry at large, it would create the perfect synergy between desktop and mobile devices, and certainly seems realistic in terms of being a part of our digital future.