Why did the Ghost of Christmas Past in A Christmas Carol look the way he did?

It was Dickens way of using the Ghost to Illuminate the mistakes made by Scrooge in the past so that they can be mended or at least so that they will not be repeated. Scrooge tries to squelch this light by use of the extinguisher the ghost carries when he feels that the ghost has shown him more than he can bear. The weight of Scrooge's mistakes is so heavy that he extinguishes the light so that he can see no more.