Shown with the two tablets containing the ten commandments in his right hand, Moses represents the Law. His presence in the window, though he doesn’t figure in the genealogy of Jesus, indicates that Jesus has fulfilled the demands of the Law, and also that like Moses, he was a Lawgiver who gave us a new Law and Testament.
Moses is portrayed in the window with rays of light coming from his forehead arranged as two sheaves. This convention, often followed in medieval times, arose from the description of Moses in Exodus 34 v29: “When Moses came down from Mount Sinai … he did not know that the skin of his face shone because he had been talking with God”. The Hebrew verb “shone” is derived from the word meaning “horn”, used sometimes to denote rays of light, and some versions of the Bible translated the word literally. Artists, by showing Moses with rays of light shaped like horns, covered both possibilities!