Old religious type takes crucial lead from nature (6)
I believe the answer is:
essene
'old religious type' is the definition.
(the Essenes were an ascetic Jewish sect)
I cannot understand how the rest of the clue works.
(Other definitions for essene that I've seen before include "Jewish frater" , "Old Jewish sectarian" , "Ascetic type" , "Member of Dead Sea Scrolls sect" , "Zealot" .)