Article on first believer in god (6)
I believe the answer is:
theist
'believer in god' is the definition.
(I've seen this before)
'article on first' is the wordplay.
'article' becomes 'the' (the definite article in English).
'on' says to put letters next to each other.
'first' becomes 'ist' (ist resembles tst).
'the'+'ist'='THEIST'
(Other definitions for theist that I've seen before include "Believer in a god or gods" , "Person who believes in the existence of a god" , "One believes in the existence of a god or gods" , "Tithes for believer in God" , "Person in good faith" .)