Subject of article — Simeon's heart (5)
I believe the answer is:
theme
'subject' is the definition.
(theme can mean a topic or subject)
'article aeur simeon's heart' is the wordplay.
'article' becomes 'the' (the definite article in English).
'aeur' becomes 'm' (I can't explain this - if you can you should believe this answer much more).
'heart' says to take the centre.
The middle of 'simeons' is 'e'.
'the'+'m'+'e'='THEME'
'of' is the link.
Can you help me to learn more?
(Other definitions for theme that I've seen before include "Topic; melody" , "Topic, leitmotif" , "Leitmotiv" , "notedly subject to variation" , "Melody on which variations are constructed" .)