ITCZ:
Just a minor correction... In a modern FMS-driven airplane, the FD also tells the AP what to do to make the airplane go where/how the MCP and FMS want the airplane to go. While you may follow the FD bars on the ND when hand-flying, the AP also follows the signals that move those bars when it is connected.
When "FD" shows on the ND, the FD expects you to do the work. When "COMMAND" shows, the AP is taking the commands from the FD.