Returning quietly, do penance in church and vacant tomb (8)
I believe the answer is:
cenotaph
'vacant tomb' is the definition.
(a cenotaph is an empty tomb)
'returning quietly do penance in church' is the wordplay.
'returning' shows that the letters should be reversed in order.
'quietly' becomes 'p' (p for piano and quiet).
'do penance' becomes 'atone' (to do penance is to atone for something).
'in' means one lot of letters goes inside another.
'church' becomes 'ch' (common abbreviation).
'p'+'atone'='patone'
'patone' backwards is 'enotap'.
'enotap' placed within 'ch' is 'CENOTAPH'.
'and' acts as a link.
(Other definitions for cenotaph that I've seen before include "Empty tomb" , "War memorial" , "Feature of Whitehall" , "Whitehall monument" , "Monument to those killed in war" .)