Reduce tempo for church sermon (6)
I believe the answer is:
speech
'sermon' is the definition.
(thesaurus)
'reduce tempo for church' is the wordplay.
'reduce' means to remove the last letter (I've seen 'reduced' mean this).
'tempo' becomes 'speed' (I've seen this before).
'for' is a charade indicator (letters next to each other).
'church' becomes 'ch' (common abbreviation).
'speed' with its final letter taken off is 'spee'.
'spee'+'ch'='SPEECH'
(Other definitions for speech that I've seen before include "'Utterance, talk (6)'" , "Giving address" , "Formal talk to an audience" , "Oral form of communication" , "Verbal communication" .)