Churchman? I too falling short in committing this? (6,3)
I believe the answer is:
'committing this?' is the definition.
The definition suggests a singular noun which matches the answer.
'churchman? i too falling short in' is the wordplay.
'churchman?' becomes 'ven' (abbreviation for The Venerable).
'too' becomes 'also' (synonyms).
'falling short' means to remove the last letter.
'also' with its last letter removed is 'als'.
Can you help me to learn more?
(Other definitions for venial sin that I've seen before include "Pardonable spiritual offence - not mortal" , "wrong, but forgivable" , "Minor offence against morality" .)