The Four Elements in the World, in Humans, and in Jews
How do the spiritual Sephirot correspond to the Holy Tongue letters? What does each letter symbolize?

Creation consists of four elements: fire, air, water, and earth, corresponding to the four letters of Hashem. These elements comprise the speaker, the living, the plant, and the inanimate, which also correspond to the four letters of Hashem. In "Etz Chaim," it is explained that even the inanimate is composed of all four elements, but its primary element is earth. The plant's primary element is water, the living is primarily air, and the speaker is primarily fire.
Now we understand the internal difference within the 'speaker' itself, which is the descendants of Jacob chosen by Hashem and the righteous converts joining them, versus the other nations of the world, who are also included in 'speaker.' The speaker corresponds to the letter yud (י) in the name of Hashem. Just as there is the body of the yud and the tip of the yud, so in the speaker, there are people from other nations who are like the body of the yud, and there are descendants of Jacob who are akin to the tip of the yud, corresponding to the world of Adam Kadmon (A"K).
The explanation is that all humanity is the crown of creation, and the sages said, "Beloved is man, for he was created in the image, as it is written in the image of Hashem He made man." However, Hashem chose the seed of Abraham, who stood by his faith against the world, and threw himself into the fire not to betray his Creator and stood through the ten tests, to be His treasured nation, a kingdom of priests and a holy nation, as a royal entourage in relation to the distinguished and beloved citizens of the state. And He told Abraham, our forefather, that among his children, "Isaac will be your seed," as the heir continuing his father's high status. The greatness passed from Isaac to Jacob after he bought the birthright from his brother and was confirmed by his father and Esau's angel. From Jacob's descendants, the Jewish people was built.
This choice by Hashem for the Jewish people is not expressed in an outward, symbolic prestige, but in an essential change with additional levels in the Jewish soul, as explained in the words of Rabbi Chaim Vital mentioned below (a non-Jew, if he truly desires, can receive this addition through proper conversion and acceptance of Torah obligations). Therefore, the nations are commanded only seven commandments, directed at rectifying the seven parts of the human body (head, two arms, chest, two legs, and the foundation place), which are seven basic commandments for a human beloved for being created in the image and his status as a citizen in the kingdom of the world's King. However, Israel was commanded 613 commandments, containing 248 positive commandments aligned with the 248 organs of the human body, and 365 negative commandments aligned with the 365 bodily sinews. As per the Jewish spiritual greatness, as one counted among the royal entourage, so is he required to behave with royal customs, not to eat everything, wear everything, or marry anyone. The greater the demand, the greater the elevation and greatness, reward and punishment.
Here are the words of Rabbi Chaim Vital in explaining the spiritual difference between the seed of Jacob and the righteous converts versus the nations, with additional tables to clarify things:
It is found that the roots of the Jewish soul begin from the highest worlds. Therefore, a commandment or, heaven forbid, a transgression done by a Jew operates and affects places that a non-Jew cannot reach. Rabbi Chaim of Volozhin expressed in the full force of truth, putting the Jew on the recognition of his greatness from one side, and on his great responsibility from the other. Here are his words in his book "Nefesh HaChaim":
"Every Israelite should not say in his heart, heaven forbid, what am I, and what is my strength to influence with my actions... In truth, the wise person who understands this in its truth, his heart quakes within him with fear and trembling when he puts his heart to his actions that are not good, how far they reach to damage and destroy with light sin, heaven forbid, much more than Nebuchadnezzar and Titus destroyed. For Nebuchadnezzar and Titus did not make any damage and destruction above with their actions, for they have no part or root in the upper worlds to touch there with their actions at all. ...because our transgressions destroyed an upper realm, holy upper worlds. And they destroyed only lower realms."
Details of the Sephirot in parallel to the letters
Above, it was explained that the ten Sephirot construct the twenty-two letters and illuminate through them, and apart from each letter being composed of all ten Sephirot, each letter also corresponds to a specific Sephira, which is the root of its action. Now, let's detail the root of each letter according to what is explained in the Book of the Image.
The first ten letters correspond parallel to the structure of the ten Sephirot:
The first three letters correspond to the first three Sephirot, which are against the head, standing separately above the body in a person.
The letter A hints at the Sephira of Keter Elyon.
The letter B hints at the Sephira of Chochmah and the letter G to the Sephira of Binah. The Sephirot of Chochmah and Binah correspond to the two parts of the brain, the right hemisphere, and the left hemisphere. While the Sephira of Keter stands above them, all three together as an inverted Segol. Just as the crown rests on the human head and encompasses the brain, so the letter A is elevated above the body of creation and emanates the letters B and G, which correspond to the brain in the head itself.
The letter D hints at the Sephira of Da'at, which sometimes comes in the count of the first three Sephirot, after Chochmah and Binah (instead of the Sephira of Keter preceding Chochmah and Binah). The place of the Sephira of Da'at is between the two parts of the brain below, as the lower point of the Segol.
Indeed, in the human brain, wisdom (to the right of the brain, in the aspect of male) elevates the idea as creation of something from nothing, and understanding (to the left of the brain, in the aspect of female) accepts the basic idea and builds it by combining details from the wisdom's repository until creating the idea's form. Meanwhile, Da'at is the final decision, akin to the realization of the world of action, which is the fourth world corresponding to the fourth letter, the letter D.
In other words, the first three are:
Keter
Chochmah Bina
or
Chochmah Bina
Da'at
The Vilna Gaon explained that the high and hidden governance is great mercy, in the aspect of the covered interiority and the great concealment, which will be revealed only in the future, is the Sephira of Keter (like an elevated royal crown that is not part of the body itself). Meanwhile, the external and revealed governance seen now is called the Sephira of Da'at.
In "The Book of the Image" it is further explained to which Sephira each letter is connected:
Keter A
Chochmah B
Binah G L N K Sh
Chesed D M
Gevurah E T
Tiferet V
Netzach Z Tz
Hod H
Yesod T A R
Crown (Malchut) Y K S P
Thus, it is found that the first ten letters, from A to Y, correspond to the ten Sephirot in their order, and the rest of the letters correspond to different Sephirot.
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