Suppose leader of Wesleyans lost faith (4,2)
I believe the answer is:
what if
'suppose' is the definition.
(both might be said before a hypothesis)
'leader of wesleyans lost faith' is the wordplay.
'leader of' says to take the initial letters.
'lost' indicates anagramming the letters.
The initial letter of 'wesleyans' is 'w'.
'faith' anagrammed gives 'hatif'.
'w'+'hatif'='WHAT IF'
(Other definitions for what if that I've seen before include "Hypothetical situation" , "hypothetical question" , "Suppose" , "How would it be when (something happened?)" , "How would things go when" .)