What is the Function of the Command Class?
The Controller tier is represented by the Command class. Commands are stateless, short-lived objects used to perform a single unit of work within an application. Commands are appropriate for communication between application tiers and are able to send system events that will either launch other Commands or be received by a Mediator to perform work on a View Component in response to the event. Commands are an excellent place to encapsulate the business logic of your application.
Reference MVCS Implementation