Manifesto for Agile Software Development second statement is about valuing working software over documentation and over things.
This is so simple and logical, it may even seem obvious: software development should be about software that works. However, this is a new idea offered by Agile movement, and not the default choice in the contract-driven Waterfall environment.
The business of software development involves many different tasks, many of which are not as complex and unpredictable than building working software. Creating documentation is a common example of such a task. It is tempting to deliver on those tasks and to declare victory based on easier-to-achieve results. It takes a lot more discipline to execute on the more complicated, core portion of the work required to create software - and deliver no less than the working software.
Delivering working software is raison d'être for the industry. It is fundamental that working software is created and delivered, and it should be the focus of the industry - not documentation, nor other more or less significant artifacts.