Christ in Glory is the huge and magnificant tapestry which hangs behind the altar in the new Coventry Cathedral, thus acting as a reredos. I read that the latter can be a painting or hanging and does not have to be wood or stone. Backs in sense of a backdrop to the exercise (in the sense of doing) of rites (homophone). I put the question mark in as Christ in Glory is a def by example, though maybe it's too far away.