Religious type: train spotter with a New Testament (10)
I believe the answer is:
protestant
'religious type' is the definition.
(I've seen this before)
'train spotter with a new testament' is the wordplay.
'train' indicates an anagram (to train can mean to grow something into a shape).
'with' means one lot of letters go next to another.
'new testament' becomes 'nt'.
'spotter' anagrammed gives 'protest'.
'protest'+'a'+'nt'='PROTESTANT'
(Other definitions for protestant that I've seen before include "Member of a church separating from Rome at the Reformation" , "A Christian" , "Member of church founded on the principles of the Reformation" , "religious type" , "expressing dissent" .)