Why " the rank and file" means ordinary?

Question

Why " the rank and file" means ordinary?

Answer 1

Rank and file...refers to the ranks that march in military formations...these are the enlisted men, or privates: equivalent to ordinary soldiers.
The officers usually march in front of their men, but are not in the formation itself, rather in front or to one side...
That is the reason the phrase is used to represent "ordinary".

Answer 2

That was the army that was marching which are the enlisted...Not the officers...which are the bulk of the army