This panel was originally in the north transept of Milan Cathedral in Italy. The window that it came from had scenes from the Life of St John of Damascus. This was designed and made for the Milan pharmacists' guild by Niccolò da Varallo, one of the principal glass painters working in the cathedral in the late 15th century. Documents record that the project began in 1479.

In the mid 19th century a great deal of restoration work was carried out on the window. It seems that this panel and two others were removed. The other two panels are now in the Isabella Stewart Gardner Museum in Boston, Massachusetts.

The image on this panel shows the great theologian and monk St John of Damascus. He is pleading his innocence against the accusations of the seated Byzantine emperor, who had received a letter falsely incriminating him. Below are the saint's words 'Testis est michi deus' ('God is my witness'). Other panels still in the window continue the story, where John's right hand is cut off and hung over the city gate. Finally, the Virgin Mary restores it to him.

St John of Damascus, a monk living in Syria, was born about 657 and died about 749. He opposed a decree of the Byzantine emperor, who was based in Constantinople (later called Istanbul), forbidding the veneration of holy images. St John's defence of images hinged upon his writings on the divine nature of Christ. Since God had taken human form, images were permissible.