Composer — American — pens introduction to concerto for God (7)
I believe the answer is:
bacchus
'for god' is the definition.
(Bacchus is an example)
'composer american pens introduction to concerto' is the wordplay.
'composer' becomes 'bach' (Johann Sebastian Bach).
'american' becomes 'US' (abbreviation for United States).
'pens' means one lot of letters goes inside another (inserted letters are held or penned in).
'introduction to' suggests taking the first letters.
The initial letter of 'concerto' is 'c'.
'bach'+'us'='bachus'
'bachus' enclosing 'c' is 'BACCHUS'.
(Other definitions for bacchus that I've seen before include "Roman god of wine and revelry" , "Greek god of booze" , "Greek god of boozing" , "Roman god of drink and revelry" , "Another name for Dionysus, Greek god of drink" .)