Soldiers calling for forgiveness of sins (9)
I believe the answer is:
remission
'forgiveness of sins' is the definition.
'soldiers calling' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'calling' becomes 'mission' (I've seen this before**).
're'+'mission'='REMISSION'
'for' is the link.
(Other definitions for remission that I've seen before include "Slackening, abatement" , "Pardon" , "Lessening of a term of imprisonment" , "prison sentence is cut" , "Reduction of sentence" .)