Mature writer follows scripture lessons (5)
I believe the answer is:
ripen
'mature' is the definition.
(ripening is a kind of maturing)
'writer follows scripture lessons' is the wordplay.
'writer' becomes 'pen' (I've seen this before).
'follows' means one lot of letters go next to another.
'scripture lessons' becomes 'ri' (I am not sure about this - if you are sure you should believe this answer much more).
'pen' put after 'ri' is 'RIPEN'.
Can you help me to learn more?
(Other definitions for ripen that I've seen before include "Grow mature like fruit" , "Become ready for picking" , "Become ready to harvest" , "Become ready to pick" , "Mature, age" .)