Bless errant ancestor entering church ... (10)
I believe the answer is:
consecrate
'bless' is the definition.
('consecrate' can be a synonym of 'bless')
'errant ancestor entering church' is the wordplay.
'errant' is an anagram indicator (I've seen this in other clues).
'entering' indicates putting letters inside.
'church' becomes 'ce' (abbreviation for Church of England).
'ancestor' with letters rearranged gives 'onsecrat'.
'onsecrat' put inside 'ce' is 'CONSECRATE'.
(Other definitions for consecrate that I've seen before include "Make 18 [SACRED]" , "giving cause to be respected" , "Bless" , "Make holy" , "Sanctify" .)