Why must I not quote a string variable when running it as a command?

My Ubuntu/Debian-based Linux update POSIX shell script seems to require that I **not double quote** the string variable with the stored command, which is being executed. As I don't understand this issue, I'd like to ask why that is? And if the code is correct as it is? Warning: SC2086, wiki , "Double quote to prevent globbing and word splitting." The script follows, the problematic part is highlighted: #!/bin/sh # exit script when it tries to use undeclared variables set -u # color definitions readonly red=$(tput bold)$(tput setaf 1) readonly green=$(tput bold)$(tput setaf 2) readonly yellow=$(tput bold)$(tput setaf 3) readonly white=$(tput bold)$(tput setaf 7) readonly color_reset=$(tput sgr0) # to create blocks of texts, I separate them with this line readonly block_separator='----------------------------------------' step_number=0 execute_jobs () { while [ ${#} -gt 1 ] do job_description=${1} job_command=${2} step_number=$(( step_number + 1 )) printf '%s\n' "Step #${step_number}: ${green}${job_description}${color_reset}" printf '%s\n' "Command: ${yellow}${job_command}${color_reset}" printf '%s\n' "${white}${block_separator}${color_reset}" # RUN THE ACTUAL COMMAND # ShellCheck warns me I should double quote the parameter # If I did, it would become a string (I think) and I'd get 'command not found' (proven) # As I don't understand the issue, I left it as I wrote it, without quotes ### shellcheck disable=SC2086 if sudo ${job_command} # then printf '\n' else printf '%s\n\n' "${red}An error occurred.${color_reset}" exit 1 fi shift 2 done } execute_jobs \ 'configure packages' 'dpkg --configure --pending' \ 'fix broken dependencies' 'apt-get --assume-yes --fix-broken install' \ 'update cache' 'apt-get update' \ 'upgrade packages' 'apt-get --assume-yes upgrade' \ 'upgrade packages with possible removals' 'apt-get --assume-yes dist-upgrade' \ 'remove unused packages' 'apt-get --assume-yes --purge autoremove' \ 'clean up old packages' 'apt-get autoclean'