Memento of priest found in church (5)
I believe the answer is:
relic
'memento' is the definition.
(I've seen this before)
'priest found in church' is the wordplay.
'priest' becomes 'eli' (biblical figure).
'found in' indicates putting letters inside.
'church' becomes 'RC' (abbreviation for Roman Catholic).
'eli' inserted within 'rc' is 'RELIC'.
'of' is the link.
(Other definitions for relic that I've seen before include "Left over item, sometimes sacred" , "Heirloom" , "Venerated remains" , "One interestingly old" , "Object of reverence" .)