Normally, when you speak a command and VoiceAttack is listening, the command is executed. When VA is NOT listening, spoken commands are ignored. So, if you issue a command to turn off listening, all spoken commands should be ignored from that point on. Which means that normally you could not ever issue another spoken command to start VA listening. In order to get around that explicit 'limitation', if you add a start listening action as the FIRST action in your command, VA will act like listening was already on and execute the command. So, in a nutshell, in a normal world, you would not be able to turn listening back on with a spoken command. But, with this, 'trick', you can get around it.
From the help document:
'Make VoiceAttack Start Listening' Select this item if you want VoiceAttack to start listening. This is useful either by itself or in a macro. Note that there is a button the Main screen as well as a hotkey for this
same action (See 'Options Screen' and 'VoiceAttack's Main Screen'). Also, note that if a, 'Start Listening' action is found AS THE FIRST ACTION within a command, the entire sequence will be executed as if VoiceAttack is already, 'listening'.