I think he is planning on making a nest on your mantle. I have seen birds "fight" their reflection in window panes, but he does want to get inside. Isn't nature grand.
He will keep doing it until he kills himself. It's mating season and he thinks his reflection is another male that he is fighting with. Tape a piece of tin foil onto your window and that should scare him away......and spare his life!
One way to prevent birds from flying into windows is to cut out the silhouette of a flying hawk and tape it to the window(s). This method is used extensively at wildlife care centers, museums, etc.
I think I'll need to take some of this advice too. I've heard no less than five birds fly into my glass enclosed front porch this morning. They sound like rocks hitting!
Although that is one cute little robin running up and down your window.