Revolutionary content of padre's letters spread the gospel (8)
I believe the answer is:
preached
'letters spread the gospel' is the definition.
I can't tell whether this defines the answer.
'revolutionary content of padre's' is the wordplay.
'revolutionary' becomes 'Che' (Che Guevara).
'content' indicates putting letters inside.
'of' indicates anagramming the letters (the answer comes from or 'of' the letters).
'padre' with letters rearranged gives 'pread'.
'che' going into 'pread' is 'PREACHED'.
Can you help me to learn more?
(Another definition for preached that I've seen is " gave address".)