To deceive the church head is to do wrong (3)
I believe the answer is:
cod
'to deceive' is the definition.
(codding is a kind of deceiving)
'church head is to do wrong' is the wordplay.
'head' says to take the initial letters.
'is to' is a charade indicator (letters next to each other).
'wrong' indicates anagramming the letters.
The initial letter of 'church' is 'c'.
'do' with letters rearranged gives 'od'.
'c'+'od'='COD'
'the' is the link.
(Other definitions for cod that I've seen before include "Pay when you get the goods - sounds fishy" , "Hoax (sl.); fish" , "A fish; a hoax (slang)" , "Fish noted for liver oil" , "method of payment" .)