When we set out to write software, it is with intent. That intent encompasses processes, rules, and requirements. The combination of all of these could be described as a summation of intent.
Maintaining software is expensive. When you design an implementation, you (should) think about what is likely to change when making your design decisions. The greater the probability or frequency of change, the easier it should be to make those changes.
When you can change the behavior of an application without recompiling the application, you significantly reduce the effort required to define,develop,test and deploy an update to the application.
http://tynerblain.com/blog/2007/09/11/why-separate-rules-from-requirements/
