I don't think it's much different than the library situation with most other programming languages.
The one big difference is that Lisp libraries can add new controls structures to the language in ways that most language's libraries can't.
For example, in Python, I can fetch a website using the stdlib's http.client, or I can use the more convenient functions from the Requests library.
In Lisp, I can iterate and loop using the built-in "loop" construct, or I can use the more convenient control structures defined in the Iterate library.
The one big difference is that Lisp libraries can add new controls structures to the language in ways that most language's libraries can't.
For example, in Python, I can fetch a website using the stdlib's http.client, or I can use the more convenient functions from the Requests library.
In Lisp, I can iterate and loop using the built-in "loop" construct, or I can use the more convenient control structures defined in the Iterate library.