A business analyst facilitates change in an organization.
The facilitation of the change is done through the facilitation of decisions. The decision could be for changes in the business processes, or the selection of tools and applications, or the creation of new applications.
All of these things come down to decisions and all those decisions are for a change from the current state. That is why understanding and documenting the current state is so important. The current state forms the basis for all those decisions.