Faith in mate and his piercing message (8)
I believe the answer is:
buddhism
'faith' is the definition.
(I know that Buddhism is a type of faith)
'mate and his piercing message' is the wordplay.
'mate' becomes 'bud' (short for buddy).
'and' is a charade indicator (letters next to each other).
'piercing' is an insertion indicator (some letters pierce a hole in others).
'message' becomes 'dm' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'his' placed into 'dm' is 'dhism'.
'bud'+'dhism'='BUDDHISM'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for buddhism that I've seen before include "philosophy" , "Major world religion" , "Religion founded by Indian philosopher Gautama" , "Philosophical faith" , "Asian religion based on teachings of Gautama" .)