An Idle mind is the Devil's workshop

I have been thinking of the meaning of this often quoted saying, "An idle mind is the Devil's workshop". I have used it in my discussions far too often. But is this saying correct at all? Whoever coined it must have been surprised at its acceptance as, in truth, it does not make sense at all. Allow me to explain this by dissecting this sentence word by word.

Workshop is a place where things are manufactured. In this sentence 'the mind' is the workshop. The products of course are the thoughts, good, bad and neutral.

Devil is the representative of evil. So if the Devil were to work in the mind workshop the product is bound to be evil thoughts. This sentence seems to suggest that the Devil can work his evil magic only when the mind is idle.

Idle means not working or inactive.

Mind is more difficult to understand and explain. What is mind? We all know and have seen the brain. But can we see mind? No. Because it is the functional part of the brain.

So far, so good.

Now looking at the sentence as a whole, does it really mean anything?

It is said that the brain needs rest and sleep. But the mind does not. It is forever active even in the sleep. In other words, it is never idle. Even when thinking evil thoughts it is working. So the 'idle mind' truly does not exist. So there is no question of the Devil entering the workshop if it can only enter it when the mind is idle. That is why I think the whole statement is wrong.

What perhaps would have been more appropriate would have been this: An idle man is the Devil's workshop. This includes both his thoughts and actions and would be a correct statement and make more sense.