Answer:
This is what I would answer if it were my assignment:
The main idea is about this person who captured a moment that was very valuable to them. The clues show because of the detail with which he remembers the day. The last line shows that the person has the picture above the fireplace, and that is usually a room that people associate with family, and happy warm memories and people will see things there. So that is a precious place to put something
Hope this helps :)