What is the origin of the idiom "in a body" and when to use it?

The idiom "in a body" originated in the 16th century and has its roots in Middle English. The word "body" in this context refers to a collective group or a gathering of individuals. This idiom can be used in various occasions and contexts, such as political gatherings, protests, marches, or any scenario where a group of individuals acts as a single entity.