Clergyman converts half the valley with one evangelistic meeting (7)
I believe the answer is:
revival
'evangelistic meeting' is the definition.
'revival' can be an answer for 'meeting' (thesaurus). I'm not certain of the 'evangelistic' bit.
'clergyman converts half the valley with one' is the wordplay.
'clergyman' becomes 'rev' (I've seen this before).
'converts' indicates an anagram.
'half the' suggests halving the letters.
'with' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'valley' cut in half is 'val'.
'val'+'i'='vali'
'vali' is an anagram of 'ival'.
'rev'+'ival'='REVIVAL'
Can you help me to learn more?
(Other definitions for revival that I've seen before include "Bringing back to prominence" , "Renaissance - renewal" , "A return to fashion or use" , "New production of old play" , "Resuscitation" .)