Sermon given by many in pious fashion (6)
I believe the answer is:
homily
'sermon' is the definition.
(homily is a kind of sermon)
'in pious fashion' is the wordplay.
'in' means one lot of letters goes inside another.
'pious' becomes 'holy' (both mean religious).
'fashion' becomes 'mi' (I can't justify this - if you can you should believe this answer much more).
'holy' enclosing 'mi' is 'HOMILY'.
'given by many' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for homily that I've seen before include "Lecture on a moral topic" , "Sermon on a moral issue" , "Edifying discourse" , "Moralising lecture" , "Sermon on a religious topic" .)