Why can't you understand what doctors are talking about when they talk shop?
Doctors cannot be understood when they talk shop because they use a language all their own. As with any discipline, those who live and breathe a field speak in specialized terms; someone outside that field cannot comprehend it, just as a layman cannot follow an M.D.'s conversation.
Les explains that a layman like him trying to converse with an M.D. shows their languages are just not the same. He asks whether anyone has been among two or three M.D.s and tried to comprehend what they are talking about; if they are talking shop, you and I get nothing out of it because they are talking a language all their own. He compares this to farmers: bring him in with a bunch of farmers, and outsiders usually do not understand them either. When people talk shop of what they live and breathe, someone from another discipline cannot understand it. Les then magnifies this into the spiritual versus the natural, pointing to Paul at Athens and Mars Hill, where the plaque honors Paul the babbler rather than the Greek philosophers.