Before end of sermon, religious leader to speak for ages (6,2)
I believe the answer is:
rabbit on
'speak for ages' is the definition.
'before end of sermon religious leader to' is the wordplay.
'before' means one lot of letters go next to another.
'end of' indicates one should take the final letters.
'religious leader' becomes 'rabbi' (I've seen this before**).
The final letter of 'sermon' is 'n'.
'rabbi'+'to'='rabbito'
'n' after 'rabbito' is 'RABBIT ON'.
(Other definitions for rabbit on that I've seen before include "talk at length" , "waffle" , "Chatter" .)