The topic of the closed door in art is abundant. Many artists were fascinated from the mistery and the symbolism of a closed door. Ghiberti made one of the most impressive examples in the Renaissance, then Donatello chose the same motive for his "Annunciation". Maybe one of the most popular doors comes from Rodin: "The Gates of Hell" highlight Dante's Inferno as a romantic source of inspiration. 
In my personal version, the primary source is Ghiberti's "Porta del Paradiso" in Florence. Instead of the biblical scenes I have painted images that describe the burning issues of our time (climate change, the power of the empires, violence and revolutions, wars...), and instead of the saints and the prophets on the sides, I have painted artists and intellectuals who have influenced or represented the course of the modern Western history from my personal point of view (all in all, 44 heads and statues). They also give us the key to understand and foresee the development of the new millenium ahead... and open that door without fear.
Here below the complete list for each single door leaf: 
 
Left (counterclockwise):
 
Laura Bassi
Frida Kahlo
Nan Goldin
Edie Sedgwick
Marie Curie
Vandana Shiva
Clara Immerwahr
Leni Rifenstahl
Anguissola Sofonisba
Alda Merini
Artemisia Gentileschi
Ulrike Hermann
Elizabeth Jennings Graham
Naomi Klein
Mary Wollstonecraft
George Sand
Sara Teasdale
Ada Lovelace
Virginia Wolf
Elena Lucrezia Corner Piscopia
Mary Shelley
 
Right (counterclockwise):
 
George Seurat
Filippo Brunelleschi
Aldous Huxley
Galileo Galilei
Bertrand Russell
Marcel Duchamp
Roland Barthes
David Graeber
Baruch De Spinoza
Charles Darwin
Marshall McLuhan
Mohandas Karamchand Gandhi
Daniele Ganser
Martin Luther King
Karl Polanyi
Leonardo da Vinci
Edward Snowden
Sigmund Freud
Noam Chomsky
Giordano Bruno
Gerhard Richter
 
There are two more heads, actually... one is mine and it is in place of Ghiberti's own head on the original door...