Assemble men, say, to visit priest (10)

'assemble' is the definition.
(I know that assemble can be written as foregather)

'men say to visit priest' is the wordplay.
'men' becomes 'OR' (military abbreviation for Other Ranks).
'say' becomes 'eg' (both can mean for example).
'to visit' indicates putting letters inside.
'priest' becomes 'father' (father is the title for a priest).
'or'+'eg'='oreg'
'oreg' put within 'father' is 'FOREGATHER'.