Musar על ברכות 15:18

From all this we can understand the greatness of occupation with Torah. And Chazal have already said: "The Holy One Blessed be He has in His world only the four ells of halachah alone." That is, the [ultimate] end of the will and the desire of the Holy One Blessed be He in His world is only the man who occupies himself with halachah, whose space is four ells.

The details of the construction of the Holy Ark, allude to one's pre-occupation with Torah and those who study it, and how they should conduct themselves. All the measurements given for the Holy Ark are expressed in terms of fractions of cubits. Its length is two and one half cubits, its width one and one half cubits, and its height one and one half cubits. This is a hint that those who study Torah should practise modesty, humility, and that they should relate to it with a broken heart. They must not brag about their accomplishments as scholars. The combined length and depth of the Ark was four cubits, its height including the lid was ten handbreadths. This alludes to the Ineffable Name which is 4 (letters) wide; when you spell the name as words: יוד-הא-ואו-הא, you have ten letters. Our sages (Sukkah 5) have said that the שכינה does not descend to a within closer than ten handbreadths from earth. When it has descended to that level it can be presumed to rest over Israel. The mystical dimension of 4 cubits, is the four cubits of הלכה which are what G–d retains on this earth since the destruction of the Temple.

Anyone while dwelling in ארץ ישראל must take to heart the lesson that he must be like a stranger in that land; only in such a way will he merit his place in the World to Come. This is what is meant by Ketuvot 111 that anyone who walks a distance of four cubits in the Holy land is assured of his share in the Hereafter. The significance of the "four cubits" is that someone progresses within the ארבע אמות של הלכה; he who has made his guiding principle in life the adherence to Halachah will enjoy such a future. G–d Himself is described by our sages as having retained only the four cubits of Halachah on earth ever since the destruction of the Holy Temple (Berachot 8). A person who conducts himself in that fashion merits an abode in the ארץ ישראל העליונה, about which it is written ועמך כולם צדיקים לעולם יירשו ארץ, Your people are all righteous, they will inherit the earth forever" (Isaiah 60,21). The reference is to the Hereafter, a region "opposite" the ארץ ישראל on earth. G–d told Abraham these glad tidings when He said to him (Genesis 15,15) ואתה תבא אל אבותיך בשלום, תקבר בשיבה טובה, "And you will join your fathers in peace and be buried in a ripe old age." The word שלום refers to Abraham entering the World to Come immediately after his death on this earth, whereas the word טובה is an allusion that the earth, the country he will be buried in, is a "good" land, i.e. ארץ ישראל. The reason it is called "good" is that anyone buried in that land will be spared the wanderings of the bones of his body until they come to rest in ארץ ישראל (Ketuvot 111). All of the aforesaid was revealed to Abraham in the first recorded communication to him from G–d when he was seventy years old. We have previously referred to this period as ראשית הבריאה, the "beginning" of creation, i.e. the first "day."

The Holy Ark containing the tablets which form the crown of Torah need not be presumed lost; it has only been concealed but continues to exist. When the Midrash quotes G–d as saying: "Make for Me a דיר, dwelling, this is an allusion to the continued existence of the Holy Ark. We are taught in Shekalim 6,3 that there were 13 spots in the courtyard of the Temple where one prostrated oneself, and that the number of such areas corresponded to the number of gates leading to the Temple. Rabbi Gamliel and the members of the house of Chananyah, the stand-in for the High Priest, however, prostrated themselves in fourteen areas. The additional spot was opposite the chamber in which the fire-wood for the altar was stored. They had a tradition that this was the area beneath which the Holy Ark had been hidden. In view of our tradition that ever since the destruction of the Holy Temple G–d has only the ארבע אמות של הלכה, "four cubits of religious law" on this earth (Berachot 8), the Midrash here quotes the full verse including the words "they shall make for Me a Sanctuary so that I may dwell in their midst." Were it not for this, the first half of the verse would not have corresponded to the latter part; in the first half the subject matter was the Sanctuary, whereas in the latter part the subject matter was Israel, i.e. בתוכם instead of בתוכו. The meaning of the verse is: "They shall make a Sanctuary for Me in order to place within it the Holy Ark which contains the tablets of testimony. This Holy Ark will continue in existence, i.e. I will continue to dwell amongst them even when the Temple itself is in ruins. My four cubits of הלכה will be present though buried." This is the crown of Torah.