You have been tasked to set up a Linux server, you have just installed the core packages of debian with debian small CD.
After installation is completed, you download two rootkit checkers:
apt-get update #To ensure you have the latest package database.
apt-get upgrade #To ensure you have the latest package with security holes patched.
apt-get install chkrootkit -y #download and install chkrootkit
apt-get install rkhunter -y #download and install rkhunter (root kit hunter)
Running rkhunter you noticed sshd allowed root access, allowing root access would give potential problem with hackers bruteforcing root password, of course you could thwart bruteforce by enforcing account lockdown for a specific period of time; however there were many ways to gain root access without knowing your password. You have decided to fix this potential problem by fixing your /etc/ssh/sshd_config.
Oh by the way ServerKeyBits 768 is kind of weak, usual RSA key length is recommended to be at least 1024-bit.
After you have made the minor changes to sshd_config you proceed to restart the service:
service ssh restart