Likutei Moharan 23:4/ליקוטי מוהר"ן כ״ג:ד׳

14. And this is the concept of meZuZah. For we find in the Midrash (Bamidbar Rabbah 22:8): Why are [coins] called ZuZin? because they ZaZ (move) from one person to the next. { “Shadai (The Almighty) will be your treasure, and money will fly to you” (Job 22:25). }

2And this is the meaning of, “Shadai will be your treasure”—that is, through the mezuzah; “and money will fly to you”—through this your livelihood will fly into your hand. This is because Shadai corresponds to the Covenant, as in (Genesis 35:11), “I am God, Shadai; be fruitful and multiply.”

3This is what our Sages expounded (Jerusalem Talmud, Berakhot 1:5): The Ten Commandments are [all alluded to] in the Shema … and the commandment “You shall not covet” (Exodus 20:14) parallels “And you shall write them on the mezuzot” (Deuteronomy 6:9; 11:20). This is because by virtue of the mezuzah, the money’s attraction is eliminated; as mentioned above: “With salt, money is lessened.” { “And ziz sadai (the bird of the field) is with me” (Psalms 50:11). }

4And this is the meaning of, “And ZiZ”—money—“SaDaI is with me.” Through guarding the brit, through mezuzah, he merits the aspect of “Zevulun, rejoice.”

5And this is what our Sages said: “And you shall write them”—the writing shall be whole (Shabbat 103b). This corresponds to (Genesis 25:27), “Yaakov was a whole person.” For through him—“And he graced the city’s countenance”—there was a rectification of the coin.

6This is also what our Sages said: Length of days is as a result of the mezuzah (Shabbat 32b). This is because juxtaposed to “And you shall write them” is [the verse] “In order that your days be lengthened” (Deuteronomy 11:21). As explained, the light of life comes from conducting business matters faithfully. And this is what they said: A verse may be expounded based on what “faces” (precedes) it (Shabbat, op. cit.). In other words, this corresponds to the Light of the Face, which is a sign of life.

7This is the reason that the mezuzah is affixed to the upper third of the doorpost (Menachot 33a). For our Sages have taught: A person should always divide his capital in thirds: a third invested in business, [a third in the ground, and a third in cash] (Bava Metzia 42a). The third invested in business is the upper third, as in the teaching of our Sages: Fifty producing more is better than two hundred sitting idle (Jerusalem Talmud, Peah 8:8).

8And faith should be mainly applied in business matters, as in (Shabbat 31a): Have you conducted your business affairs faithfully? Thus the essence of money, where one needs faith, is in the upper third—the third invested in business.