What is the origin of the idiom "good Lord" and when to use it?

The idiom "good Lord" is used to express the feeling if surprise, confusion, or amazement. While the exact origin of this idiom is difficult to trace, it has been in use for a long time in the English language, often as an interjection to react to something unexpected or astounding. This expression is commonly used in informal and spoken language to express strong emotions or reactions.