The kernel is the core of the system, whilst the shell surrounds it and is the interface between the kernel and the user.
Within any UNIX system, and even with Linux systems, the shell is the place that systems administrators work to configure and manage a system.
Modern terminology often uses the term CLI or command line interface to describe the shell prompt.
This is in deference to the GUI or graphical user interface.
However any real Sysadmin knows that you should not use GUI tools to configure a UNIX/Linux and work only directly at the shell command prompt.
This is even more relevant nowadays when we hear some junior Linux enthusiasts say things such as "I use linux, but I've not really learnt the CLI".
As the old adage goes "If you can't do it at the shell prompt, you can't do it."