Possibly so he doesn't end up like Marley.

So he can show people how grateful he is for living.

It was Scrooge's nephew.

He could not bare to see what was happening and demanded the ghost to take him home.

The ghost said he was The Ghost of Christmas Past.

He wished for happiness and pleasure.

When the bell struck one the first ghost appeared.

The reader must understand who the characters are or who they used to be. For example in this case it would be Scrooge and Marley. It would also be how the character's felt about each other.

It is normally cold, foggy, and not so bleak.

When his nephew greeted him he said "BAH HUMBUG".