I was reading an excerpt from the book 'The Last Lesson' by the French novelist Alphonse Daudet for my class when I came across the expression 'as quiet as Sunday morning'. 

My first guess was that the expression is implying that Sunday mornings are quiet because it's a holiday and everyone is at home, possibly sleeping. 

But can the expression also mean that everyone is in the church for the church service (I'm from India, so I know very little about Christianity).

Here's the expression it's proper context - 

> 
> Usually, when school began, there was a great bustle, which could be
>  heard out in the street, the opening and closing of desks, lessons
>  repeated in unison...But now it was all so still! I had counted on the
>  commotion to get to my desk without being seen; but, of course, that
>  day everything had to be **as quiet as Sunday morning**.
> 
> 
>