Sacrifice in the place of god, mainly (5)
I believe the answer is:
forgo
'sacrifice' is the definition.
(to forgo something is to give it up)
'in the place of god mainly' is the wordplay.
'in the place of' becomes 'for' (as in acting for someone in or in place of them).
'mainly' means to remove the last letter.
'god' with its final letter taken away is 'go'.
'for'+'go'='FORGO'
(Other definitions for forgo that I've seen before include "Live without" , "pass up" , "Go without (something)" , "Waive" , "Abjure" .)