Symbols can confirm or clarify themes by using something but it meaning something else that reveal the theme, for example, the theme is kindness is often overshined by greed, the symbol is a caged bird without food in a magic castle trapping a selfish, greedy prince. It is only when the prince gets board of the castle but can't go outside because of the magic spell, and realizes the bird also wants freedom, that the theme shows, or is revealed
It is false that reading a play rather than seeing it takes away all of its entertainment value. Both reading and seeing a play can be very entertaining, it has nothing to do with the medium.
