All intelligence is metaphysical and religious, by definition.
The intelligence that enables a philosopher to spew out his petty materialist platitudes [i.e Stirner, "The Ego and his Own" or Nietzsche, "The-beta-who-preached-the-Overchad."] is sufficient to comprehend the fundamental truths of metaphysics, at least partially, so as to prevent him from doing harm and wasting his time.
If Stirner were sent to Siberia, he would certainly be cured of "muh spooks and property" and become a metaphysician, or at least he would become capable of becoming one.
If you have no sacred text, if you don't study metaphysics, if you don't practice a religion based on absolute truth then what are you? Who are you? Why are you here? You are not yet fully human.
God said "let us make man in our image". All else he spoke into existence immediately and it was. But man is God's work in progress, the process started with dust of the earth and was perfected only on Cavalry where Christ sacrificed himself and said "it is finished" and thus showed us the meaning of perfect love and what it means to be divinely human.
So if you can't decide what book to read next ask yourself whether it has any metaphysical merit to it. Would a saint or sage read it?