It was Christmas Eve. I begin this way because it is the proper,
orthodox, respectable way to begin, and I have been brought up
in a proper, orthodox, respectable way, and taught to always do the proper, orthodox, respectable thing, and the habit clings to me.
Of course, as a mere matter of information it is quite unnecessary to mention the date at all. The experienced reader knows it was Christmas Eve, without my telling him. It always is Christmas Eve, in a ghost story.