Question - Why SOA?
Answer -
Service is the important concept. Services can be published, discovered and used in a technology neutral, standard form by the set of protocols of the web services.
Other than being just architecture, SOA is the policies, practices, and frameworks by which it is ensure the right services are provided and consumed.
It becomes critical to implement processes that ensure that there are at least two different and separate processes— one for provider and the other for consumer, using SOA.
The Business Service Bus is starting point for developers that guide them to a coherent set that has been assembled for their domain.
This is better than leaving developers to discover individual services and put them into context.