I love triptych. Mostly a painting that has two sides with a message: front closed and front opened. Sometimes the backside has a painting too (better: three). In the Middle Ages the front was closed most of the time - I guess - because it was their way of getting the fellow Christians eager and willing for the beauty of the mystery.
A couple of times a week, a month the triptych was opened with all it's colours and light. A very strong visual message of how to behave. Be good and you will go to paradise. Be bad and you will go to hell.
Panels closed ... for me it's the Christian way of a Chinese garden. Seduce them to the mystery.
Panels open ... for me the christians are too black and white. The image of paradise and hell in afterlife is a wrong metaphor. Simply because there is no such thing. It's our 'homo sapiens' projection of evil to the Devil and Others. The painful truth is, we are "evil" here and now. Not the Others but you, me and all other individual 'homo sapiens'. We are sweet and sour. And if we deny our sour we ...
P.S. The presented triptych 'The Garden of Earthly Delights' is from Hieronymus Bosch (around 1450-1516).