Preacher of letters overwhelmed by beer (7)
I believe the answer is:
apostle
'preacher' is the definition.
(the apostles spread Jesus' message)
'letters overwhelmed by beer' is the wordplay.
'letters' becomes 'post' (letters in the mail or post).
'overwhelmed by' means one lot of letters goes inside another (inserted letters get absorbed or overwhelmed).
'beer' becomes 'ale' (type of beer).
'post' placed inside 'ale' is 'APOSTLE'.
'of' is the link.
(Other definitions for apostle that I've seen before include "'Matthew or Mark, say (7)'" , "who can handle a spoon?" , "Divine messenger" , "Follower of Christ" , "Teacher of new faith or movement" .)