A celebrant at work in place of worship (10)
I believe the answer is:
tabernacle
'place of worship' is the definition.
(tabernacle is a kind of place of worship)
'a celebrant at work in' is the wordplay.
'at work' indicates anagramming the letters.
'in' is an insertion indicator.
'celebrant' anagrammed gives 'taberncle'.
'a' placed into 'taberncle' is 'TABERNACLE'.
(Other definitions for tabernacle that I've seen before include "Portable tent" , "Tent for the Ark of the Covenant" , "Place of worship; sacrament box" , "Tent for Ark in Exodus" , "Mormon temple" .)