The Purpose of a Rood Screen
As originally envisaged (in mediaeval times) the purpose of a Rood Screen ... “... was to divide the chancel, with its altar, from the nave, which was often used for secular purposes. It was an invariable part of the furnishing of every church until the Reformation, usually placed directly beneath the chancel arch, though sometimes brought forward slightly so that it could stretch right across the nave and aisles. The screen was generally surmounted by a loft, upon which stood the Rood, a giant figure of Christ crucified. The Reformation saw the destruction of virtually every Rood and the great majority of lofts, though the screens themselves were often spared as they were a useful feature in the ordering of the church.”
Thomas Muckley, Rood Screens in East Anglia (1995).