Paul Helm has posted an excellent little piece on what definitions do and don't do. Despite its brevity, it is a helpful meditation that can go a long way to clearing away some of the confusion.
A few quotes:
"Berkhof’s definition is not an attempt to replace the language of the Psalms or of any other language, or to be cleverer than Scripture. His definition does not take us beyond Scripture, making Scripture second-rate. It is a skeleton, not the entire body."
". . . definitions do not describe, they protect and safeguard."
"Where we are not understanding the scriptures with the skeleton of systematic theology in place then our ‘body of divinity’ will be flabby and misshapen. . . . We ‘participate’ in sound definitions when they engender confidence that they have captured the relevant bit of the skeleton."
"Calling exact, propositional theology rude names like ‘theoretical’ or ‘foundationalistic’ does not alter anything."
Upshot: "So definitions are not imperialistic. They are not the work of theological know-alls. And the theoretical versus practical issue is a red herring."
Read the whole thing!