There is recurrant theme that Satan is a mere metaphorical construct, this makes perfect sense to me, but how does it reconcile with 7th Satanic rule?
Greater Magic is a technology.
Compare it to using electricity.
Use it with respect for what works and you might get desirable results.
Abuse it with a lack of respect for what works and you may get nothing ...or worse.
Just as in driving a car you need to respect the requirements of turning an ignition key, taking off the parking brake, and putting the car in gear, with Greater Magic there are mental
actions that are required.
The first of these is to get past identifying with the aspect of the Christian God known as omniscience - already knowing everything.
Even our best "reality experts", modern physicists, are quite clear that we do not
It is possible that we never will.
Doubting that Greater Magic is impossible can be made easier by remembering that.
The suspension of disbelief in magic is a requirement
in Greater Magic. So if you cannot do that then just skip Greater Magic.
Greater Magic is only an option for the Satanist who has the talent for using it. It is not necessary.
It is another tool to be used if you have the knack for doing so.
If you can't use it right, put the tool down and leave it alone.
That just makes sense whether the tool is electrical or magical.
Read the warning label.
Wear safety goggles.
Or don't use it.