The interior of the church itself has been redone with some very nice displays. There is artwork from the movie. There are also quite a few artifacts and historical items on loan from somewhere (a museum in Norway, sorry I do not recall the name of it), on display in sealed temperature controlled cases, including handmade clothing. There's quite a bit of descriptive signage that explains how all these items and traditions inspired the artwork and story in Frozen.
I really enjoyed looking at all of it. As packed as Norway was on NYE, hardly anyone went inside the church while we were in there, so we got to look and read to our hearts' content.
There is also a photo-op area further back in Norway for the princesses.
I didn't notice any special Frozen merchandise in the Norway shop, just the usual (lovely) clothing in the back room and the normal tshirts, toys and souvenirs up front.