The term ONE DOING THE LORD'S WORK can be broken down into three crossword solutions: SERF (4 letters), PEASANT (7 letters), and LIEGE (5 letters). A SERF was a person in the Middle Ages who was bound to the land and owned by a lord, and had to work the land in exchange for protection. A PEASANT was a lower-class farmer who worked the land of a lord in exchange for rent or services. A LIEGE was a feudal lord who held land from a higher lord, and was responsible for providing military service and other duties. All three of these terms refer to people in the Middle Ages who were doing the Lord's work, either through farming or providing services.