Gaston Bachelard writes that the casket contains the things that are unforgettable, unforgettable for us, but also unforgettable for those to whom we are going to give our treasures. Here the past, the present and a future are condensed. Thus the casket is memory of what is immemorial.
The Poetics of Space, p.84

Faced with the idea of making boxes there is also the idea that the boxes will hold something.