End scene at beginning

I wonder why they showed one of the ending scenes ("Past" pushing the doll parts in the cart after his "demotion") at the beginning of the movie (the first scene inside the "Bureau of Yuletide Affairs").

I know this is a time travel movie, but not sure what the significance of doing that was.

Also, this scene at the end is shown in a round TV screen like device (actually it is one of the green Christmas tree balls hanging on the wall in the bosses, "Trevor James", office) which then turns to static and then turns off, and you can then see the mirrored reflection of Trevor James' office in the Christmas ball ornament. There is no one visible in the office. How is that significant?

I know this is no movie for deep thinkers, but I was just wondering if there was some reason I missed as to why they did these things.