Once again remodel saint in screen behind the altar (7)
I believe the answer is:
reredos
'screen behind the altar' is the definition.
I can't tell whether this definition defines the answer.
'once again remodel saint in' is the wordplay.
'once again' becomes 're' (prefix in verbs).
'remodel' becomes 'redo' (synonyms).
'saint' becomes 's'.
'in' is an insertion indicator.
'redo'+'s'='redos'
're' placed within 'redos' is 'REREDOS'.
Can you help me to learn more?
(Other definitions for reredos that I've seen before include "Fireback" , "Painted screen behind an altar" , "Wall decoration behind altar" , "Back of fireplace" , "Ornamental screen behind a church altar" .)