Question:

After the Giving of the Torah, Moses went up Mount Sinai for 40 days. After the Golden Calf, he went up another 40 days, and then he went up the final time for yet another 40 days to secure complete forgiveness from G‑d. What’s up with the number 40?

Reply:

The number 40 is actually highly symbolic in the Torah, but since you ask specifically about why Moses had to go up the mountain for 40 days and nights, I’ll address that first.

Forty Days for a Baby to Form

The Talmud explains that it takes an embryo 40 days to form in its mother's womb.1 Thus, just as it takes 40 days of preparation for a new being to emerge, so, too, it generally takes 40 days for a new spiritual entity to come into being.2

Forty Years to Comprehend

The Talmud tells us that “one does not come to fully comprehend the knowledge of his teacher until 40 years [of study].”3 Since a day “up on high” is certainly equal to a year down below, Moses learned Torah from G‑d atop the mountain for 40 days so that he could fully comprehend the Torah.4

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Other Forties: Something Deeper

If we look in the Torah, we find many other things that are associated specifically with the number 40:

  • In the episode of Noah and the Flood, we learn that it rained for 40 days and 40 nights.
  • A mikvah needs to have 40 se’ah (a measurement) of water in order to be able to purify someone. In fact, this is one of the explanations as to why, during the Flood, it rained for 40 days, corresponding to the 40 se’ah of a mikvah.
  • Regarding the maximum amount of lashes one could get, the Torah describes the amount as 40 (albeit in practice, one could get a maximum of 39).
  • According to the Talmud, it took “40 minus one”5 types of creative work to build the Mishkan (Tabernacle).

What is the common thread here? What is the symbolism of the number 40?

Transformative

The mystics explain that any preparation for a transformative change is associated with the number 40. Thus, whether it is the flood water of Noah, which cleansed and purified the world, going to the mikvah, which purifies the person, lashes, which atone for one’s sins, or receiving the Torah, each is essentially a catalyst for transformation6 and is therefore associated with the number 40.7

Why is that?

10 x 4

Kabbalah explains that all of reality can be divided into four worlds: Atzilut (Emanation), Beriah (Creation), Yetzirah (Formation), and Asiyah (Action.) These four worlds, in turn, emanate from and are rooted in the four letters of the holiest name of G‑d.

The Chassidic masters teach that the microcosm emanates from and reflects the macrocosm. Thus, there are many other sets of fours reflected in nature and creation. (For example, there are four categories of being in the natural world: domem, the inanimate; tzomeach, the vegetative; chai, the animal; and medaber, the “speaking,” i.e., human. Similarly, each individual creation is made up of four elements: earth, water, air and fire).8

Each of the four higher spiritual worlds possesses the entire spectrum of the ten sefirot, G‑d's creative attributes, which are reflected in all existence, including the human soul.9 Now, 4 x 10 = 40, so a complete category of “being” or “world” has 40 aspects. In other words, 40 represents the completion of a whole mode or way of being.10

The Ultimate Forty

The Lubavitcher Rebbe explains that just as the first time the Jews went into the Land of Israel, it was after a “preparation” of 40 years in the desert, so, too, the number 40 is associated with the final redemption.11

In the Talmud, Rabbi Eliezer says: “The messianic era will be 40 years, as it is stated: ‘Forty years will I strive with the generation.’”12 The commentaries explain that Rabbi Eliezer was not limiting the time of the messianic era. On the contrary, what he is referring to are 40 years of the “messianic era” that will precede and prepare for the Resurrection of the Dead.13 Indeed, the Zohar states that there will be “40 years” until the Resurrection of the Dead14 (or to be more precise, as the Lubavitcher Rebbe explains, it will take 40 years until the resurrection process is completed15).

May it be speedily in our days!