A possible approach to understanding Isaac Luria: (1) External and internal worlds refer to subject and object. (2) Light and vessel mean the essence of existence and characteristics.
This is different from Ashlag [note 2] who wanted to interpreted the Ari as advocating a basically communistic system
In philosophy there is one area which deals with how we know things.{note 1} And there is another area which deal with what things actually are. This later area is called Metaphysics. [The name comes from the set of books called the Metaphysics by Aristotle which deals with the question of what things actually are as distinct from their characteristics. ] And this Metaphysics also got to be divided into different areas. One is the nature of things and the other is the existence of things. And both these later areas got divided up into the question of the person looking at stuff. He is called the subject. And the objects he is looking at are called the objects.
The divisions are divided between Kant, Hegel, Berkley, and Descartes.
Kant holds characteristics of objects depend on the subject. But their existence is independent.
That is transcendental [independent of experience] idealism (dependent on my existence). This is the exact opposite of Hegel who holds from empirical realism.
My suggestion here is to understand the Ari [Isaac Luria] and the Reshash in this way of transcendental idealism. That is not to say that this is the only level on which the Ari can be understood. Rather I have always understood him to be referring to many (maybe infinite) sub-levels.
The basic idea here is that with Kant we have the existence of the subjects that is you and me and of objects being transcendent, i.e., independent of experience. But not in terms of characteristics. We can see such a thing in an electron who knows to act differently when he sees two slits in front of him or one slit. He know that is there is one slit he is supposed to act like a particle. If two slits he know to act like a wave and to interfere with himself if there are no other electrons present. This fits perfectly with Kant.
In Isaac Luria we also have these sub-divisions. The light is the essence of the thing. and the vessel is its characteristics. And the worlds are divided into inner and outer, [subject and object.]. This you can see best in diagram the Reshash has in the regular Eitz Chaim that is somehow missing in the Ashlag edition.
Now in terms of knowledge of stuff we have the exact same divisions: Kant, Hegel, Berkley, and Descartes. And that also you can see in the famous Drush Hadaat of the Reshash.
For further reading see
(2) And also the regular Eitz Chaim [Tree of Life] by Isaac Luria and Chaim Vital.
Also the Eitz Chaim printed by the Ashlag group]
(3) The only things to read in Kant are the three Critiques. The area of Moral theory which is teh only thing they teach to university students is the weakest of all of Kant's writings and anyway cant be understood without the three Critiques.
(Note 1) This area is not very interesting. It gives us "the Fundamental Fallacy of Philosophy: the idea that the limitations of our minds tell us anything about the nature of reality. What we can call The Fundamental Fallacy of Modern Philosophy might be defined as the idea that it makes sense to study structure divorced from content. This is the idea that has given us businessmen who think they can "manage" without knowing anything about what they manage, critics who claim that only the technical excellence of a work of art matters, not its content, and sociologists of science." (Steven Dutch)
(Note 2). Ashlag was influenced by Hegel and thought Communism and/or Socialism is the ideal goal.
I can't But this political position does not show up in his commentaries on the Kabalah except in rare places. At any rate, I am thinking that it is first not true that Socialism represents the ideal society. 100 million victims of Stalin, Lenin, and Communistic China would seem to prove this last point. Also, I think that Ashlag did not take into account that the Torah is highly capitalistic. How can you read the Torah and not realize private property is an essential part of it.?
I should add perhaps that Kabalah is not usually understood as an alternative to Torah but as a deeper understanding of Torah. At least that is what we get with the Zohar and the Ari and the Gra. No question people that get into it tend to start to make up their own religions. That is a sad tendency but it is I think contrary to the spirit of the authentic kabalists. I am trying to concentrate on the good aspects of Kabalah here. But I am aware of the pitfalls. If you want to avoid the pitfalls, then learn it in the general context of the Geon from Vilnius.