Now that I think about it the Tree of Life commentary is a little bit advanced. While there isn't really a "danger" for a begginer or gentile to reading it, you can't gain much from it without hours and hours of intense study.
About it being only for Jews, here is Rav Laitman's position:
"To Be a Jew
Jewishness in the Eyes of Kabbalah
Have you ever came across this line: “There is no God, and I hate Him!” The Jewishenss of Jews is probably the most sensitive issue for the Jews as a community. Being a “good Jew” is still important even to Jews who claim to be total atheists.
But what does it mean to be a Jew? If I am born to a woman who is officially Jewish, I am officially considered a Jew. But where is it mentioned that it should be like that? The Nazis didn’t think it mattered that much and killed people who were officially Christians, because their great grandfather was Jewish. Can it be that we are looking at it from the wrong angle altogether?
If we look in the Torah, the word Yehudi doesn’t appear in it, except as a name of a woman (“Judith – Yehudit - the daughter of Beeri the Hittite” Genesis 26: 34), and even she is not the daughter of a Jew. The first time there is mention of a Jewish nation is in Kings 2 16: 6 (“Rezin king of Aram recovered Elath to Aram, and drove the Jews from Elath”). When did the Jews become a nation?
Was Abraham the Patriarch the first Jew? He came from Mesopotamia, today’s south-east Iraq. What has this land got to do with Jewishness, or with Israel?
That being the case, why do we call him Avraham (Heb. The father of the nation)? We begin to unravel this riddle when we remember that Abraham was titled not the first Jew, but rather the first Hebrew (Ivri)! The first time Abraham is called Ivri is in Genesis 14: 13. But what the narrative doesn’t tell us is when he became a Hebrew, and what this title really means?
The great Kabbalist, Rabbi Baruch Shalom Halevi Ashlag (Rabash), the son of Rabbi Yehuda Ashlag (author of the Sulam commentary on the Zohar), in article No. 17 from 1991, interprets the verse “and he saw an Egyptian smiting a Hebrew” (Exodus 2:11), by explaining that an Egyptian is a person who receives for self, whereas a Hebrew is one who receives not for oneself.
Here lies the key to the secret of the origin of the Hebrews. They are not a people, they are actually a state of being! It is a changed focal point. Being a Hebrew is no longer about my ancestry, it is about who I am! The difference between being a Hebrew and being something else is described by Rabash as the difference between being like a beast, or like a human being (Adam). The word Hebrew indicates crossing over something (Ivri comes from the Over, meaning going over something). What is it that we cross over? We go over from one state of being (beastly) to another (human).
The Hebrew word Adam (human) comes from the word Adame (being like). It means being like the Upper One, the Creator. It is best expressed in the words of the prophet Isaiah (14: 14): “???? ?? ???? ?? ???? ??????” (“I will ascend above the heights of the clouds; I will be like the Most High”).
Thus, any person who succeeds in being like the Creator crosses over from being Egyptian to being Hebrew. In that regard one’s birth religion is irrelevant! It is only our inner state that determines who we are, whether we are Jews or not.
Let us assume for a moment that I examine myself, and find that I am not like the Creator. Even worse, I don’t know who He is, so how can I be like Him? How do I become like Him, and indeed why should I want to be like Him? The way begins in the desire. If I want to become like Him, I am on my way to being a Hebrew. If the thought never crossed my mind, or if it has and I declined the option, then I should at least know, that my Jewishness or Gentileness is no more than something someone has labeled me, that in no way reflects my inner state. "
^^^that is what Laitman says about whether or not Jews can study Kabbalah, I realize this position is somewhat controversial, but I agree with it. Although, Rav Laitman has also said that those who are Jews in this world (ie born as Jews externally) are obligated to study kabbalah, while those who are not born Jewish are allowed to study it but not obligated. Therefore being a Jew of this world is a responsibility, not a priviledge, you are obligated to study kabbalah so that all of mankind can advance through the Jews.