Spirit level, theosophically speaking! (6,5)

'theosophically speaking' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'spirit level' is the wordplay.
I cannot really see how this works, but
'level' could be 'plane' (plane is a kind of level) and 'plane' is found in the answer.
The remaining letters 'astral' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?