Why? If you get it fixed - you’ll have learned the skills to master those situations.
If your system doesn’t boot up anymore just use a live usb and manjaro-chroot into your existing installation to repair.
Your error message mentions /etc/pam.d/system-auth and /etc/pam.d/system-auth.pacnew.
You should inspect/merge pacnew files when the get generated - preferably before a system reboot/shutdown. See pacman/Pacnew and Pacsave - ArchWiki