Mark was a man of action - always ready to go with the windswept look and said to be the Bishop of Alexandria (note the Pharos Light in the background). I've had a chuckle over the "psychic scroll" he holds (in reference to a Doctor Who prop).
Matthew was initially a tax man hence the money box beside him on the stone bench and inkwell to mark names. The woven pattern in the edge trim is based on the bound fasces rods of Rome and the imperial purple robe.
There are little tidbits like this that go into designing while still showing these four men were regular fellows just like you and I. There was a whole library of symbolism that could be drawn on but most people are unaware of the meanings anymore of obscure figures or objects in the older windows, but I prefered to keep them simple.
Patricia Ann Daley is an artist living in Sarasota, Florida and the author of Stained Glass Step by Step (2003).
Visit her website at http://www.kaleidoscope-stainedglass.com