Girl sitting by one slope in biblical territory (8)
I believe the answer is:
galilean
'in biblical territory' is the definition.
(relating to Galilee)
'girl sitting by one slope' is the wordplay.
'girl sitting' becomes 'gal' (I am not sure about this - if you are sure you should believe this answer much more).
'by' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'slope' becomes 'lean' (I've seen this before).
'gal'+'i'+'lean'='GALILEAN'
(Other definitions for galilean that I've seen before include "from northern Israel?" , "Like some telescopes" , "Old Christian" , "As an old-fashioned Christian" , "associated with mathematician from Italy" .)