In the painting the figure is in front of a cup (also triangle void between jezus and john) in painting is like a cup. We even see Brittania holding a cup…
The cup (holy grail) is in my opinion and personal research the constellation Crater. The dragon Hydra. John is virgo/Mary.
She is also Indian Durga and Brittania. (And related to the bank of england logo. See the sheet of weat. )This we can see because of the lion. (whilst Shiva is orion with Taurus) Jesus is the sun going through the constellations. Mark and Maria are close in naming. Mark has the lion and John the chalice with the dragon. (crater/Hydra) and is depicted as the eagle.
The triptych window symbolism is directly related to the sun moving in the sky left to right rising based on season. The middle door is spring/autumn when there is an equal amount of light and darkness in the days. Hence this was balance. Ying jang. This is encoded in many pyramids and temples around the world in the doors. In ancient days this was also decoded in the 3 domes, or the two obelisks and the middle temple passage in Egypt. In later times we see this back in the ark the triumph.
This is the true meaning of the tryptich symbolism and a small piece of the puzzle why Christianity and its churhces is hidden astronomy , like the temples in India.
A further good read is this website: http://www.solarmythology.com/