The St. Luke Window
The Gospel of St. Luke concerns itself with the sacrifice, priesthood and atonement of the Saviour. Hence the ox, the animal of sacrifice. The small caduceus, serpents twined round a staff, refers to St. Luke's calling of physician.
Information on the stained glass windows comes from the book "The Windows and Symbolism of First Methodist Church, Birmingham, Michigan", edited by Dr. Arnold F. Runkel and privately published by the church for its members in 1966.