After religious instruction, heaven appears unsafe (5)
I believe the answer is:
risky
'unsafe' is the definition.
(similar in meaning)
'after religious instruction heaven' is the wordplay.
'after' means one lot of letters go next to another.
'religious instruction' becomes 'RI' (abbreviation).
'heaven' becomes 'sky' (I've seen this in another clue).
'ri'+'sky' is 'RISKY'.
'appears' acts as a link.
(Other definitions for risky that I've seen before include "Speculative" , "taking a chance" , "too adventurous" , "admitting possibility of unpleasant outcome" , "Potentially dangerous" .)