The Sefirah of Keser is comprised of two levels, one named Atik and the other Arich. Atik means “removed,” as the verse states:1 Bereishis 12:8, 26:22; Likkutei Torah, Bamidbar, p. 67b; Devarim, p. 61c. “Veyehtak mishom,” which means “And he moved from there,” or as the Targum2 translates: “And he left the place.” This is the quality of the level; though Atik is part of the Sefirah of Keser, it is essentially removed and withdrawn from the world [which Keser illuminates].
The second level in the Sefirah of Keser is Arich, which means “long.”
Matters may be lengthy or abbreviated. Though the abbreviated form [generally] represents the contents of the lengthy matter, the abbreviated version cannot compare to the matter as it is in its full length.
An example would be the Abbreviated Code of Law [of Rabbi Shlomo Ganzfried]. The Abbreviated Code of Law states the final decision on every law as it was arbitrated after lengthy discussions in the Gemara and Codes of Law. Yet the statements of law there cannot really be compared to the same laws as discussed in the Gemara and by the codifiers. For although the laws are stated in a clear a succinct manner, they lack inner illumination and life.
For example, the laws regarding family purity, training one’s child, kashrus associated with salting meat and the admixture of meat and milk are all found in the Abbreviated Code of Law. Yet all that is stated there are the bare halachic decisions; that during certain times a married woman is to conduct herself in a specific fashion, or that a young child should be trained in the washing of his hands, and should sleep with his head covered; that as soon as a child begins to speak, even though he is not yet speaking clearly, his parents should begin reciting with him the verse of Shema Yisroel. The same holds true for the laws regarding Shabbos observance, salting meat and separating meat from milk. All that is found are statements of what should and should not be done.
These same laws as found in the Gemara and as treated by the codifiers not only state the law with its underlying reason and source in the Written and Oral Torah, but also go into great detail. All the laws germane to a particular mitzvah are enumerated, as are the stringencies of each. For example, if a woman does not immerse herself at a particular time in a proper mikvah there is a prohibition which carries with it the punishment of kareis, the cutting off of the soul from its source. Also, in various Jewish books we are told of the great reward and good children born to those women who scrupulously observe these laws, and — may Heaven protect us — the severe punishments and evil offspring born to those who are not respectful of the laws. The same is true of all other laws. Yet in the Abbreviated Code of Law we find only the actual rulings.
The same holds true with regard to the Sefirah of Arich, which means “lengthy.” The Ten Sefiros beginning with Chochmah and concluding with Malchus are divided into two general categories: the three Sefiros of Intellect, Chochmah, Binah and Daas (or wisdom, understanding and knowledge); and the seven emotive Sefiros of Chesed, Gevurah, Tiferes, Netzach, Hod, Yesod and Malchus (or Kindness, Severity, Beauty/Mercy, Victory, Glory, Foundation and Kingdom). The six Sefiros of Chesed through Yesod are termed Z’eir Anpin, Small [or Abbreviated] Lights, for they are similar to the Abbreviated Code of Law, while the [lower] level in Keser is termed Arich or “lengthy,” for it is similar to the laws as stated in the Gemara and by the codifiers.
In summary: Keser is comprised of two levels, the first being Atik, which is removed from the world [illuminated by Keser], and the second Arich, which is related to that world. Arich is lengthy in comparison to the Ten Sefiros of that world, similar to the way a law appears at length in the Gemara and the codifiers, with details regarding its reward and punishment, while all that is found in the Abbreviated Code of Law is the actual legislation.