The first north transept window

The main detail shows a lamb holding a staff surmounted by a banner. The banner itself bears a red cross on a white background like the St. George’s cross. In religious art such an image is known as an Agnus Dei (Lamb of God, in Latin).

In the Christian tradition, the ultimate mission of Jesus to die on the cross to atone for our sin is analogous to the sacrifice of a lamb. John the Baptist referred to Jesus as the Lamb of God –
“Behold the Lamb of God who takes away the sin of the world!”. [John, 1:29]