Give unrestricted access to study group during worship (10)
I believe the answer is:
declassify
'give unrestricted access to' is the definition.
(as in declassifying files)
'study group during worship' is the wordplay.
'study group' becomes 'class' (group of people studying together).
'during' means one lot of letters goes inside another.
'worship' becomes 'deify' (I've seen this in another clue).
'class' inserted within 'deify' is 'DECLASSIFY'.
(Other definitions for declassify that I've seen before include "Downgrade (a secret document)" , "set in public domain" .)