This writer's describing southern student finding religion (5)
I believe the answer is:
islam
'religion' is the definition.
(I know that Islam is a type of monotheism)
'this writer's describing southern student' is the wordplay.
'this writer's' becomes 'I am' ('I am' refers to the person writing).
'describing' is an insertion indicator (describe can mean to form the outline of).
'southern' becomes 's' (abbreviation).
'student' becomes 'l' (as in L-plates for learner drivers).
's'+'l'='sl'
'iam' placed around 'sl' is 'ISLAM'.
'finding' acts as a link.
(Other definitions for islam that I've seen before include "Major world religion" , "Mohammed's religion" , "Faith with five pillars" , "Mails to Muslim religion" , "Religion based on Muhammad's teachings" .)