Theist arranged donations to the church (6)
I believe the answer is:
tithes
'donations to the church' is the definition.
'theist arranged' is the wordplay.
'arranged' indicates anagramming the letters.
'theist' anagrammed gives 'TITHES'.
(Other definitions for tithes that I've seen before include "Tenth parts, levied by some churches" , "Tenths of income given to church" , "Tenth parts, levied by a church perhaps" , "Levies of one-tenth, to church perhaps" , "Church taxes" .)