Debian is a free operating system (OS) for your computer. An operating system is the set of basic programs and utilities that make your computer run. Debian provides more than a pure OS: it comes with over 59000 packages, precompiled software bundled up in a nice format for easy installation on your machine.
Can someone explain this paragraph please?
Because of technical limitations in Linux in the 1990s, every Debian package has full root access during its installation. In other words, every Debian developer can potentially become the root user on any machine running Debian. With tens of millions of machines running Debian, that is potentially a lot of power.
The package pre and post scripts are run as root. These are the things that make sure users and groups exist and other such tweaks to the system. You are essentially trusting the packager doesn't put anything nasty in there.
because of its social contract, its free software guidelines, and the community around it