The Significance of the Number 40

(1) We have the custom to get up at the break of dawn to recite Selichot and tachanunim from Rosh Chodesh Elul until Yom Kippur.

REMA: The minhag of Ashkenazi Jews is not like that. Instead from Rosh Chodesh on we blow the Shofar after Shacharith, and there are some places where they also blow the Shofar after Arvit. We get up at dawn to recite Selichot from the Sunday before Rosh HaShanah...

(1) There is a hint in the verse “I am for my Beloved and my Beloved is for me” (Ani L’Dodi v’Dodi Li - Shir Hashirim) that the first letters spell Elul and the last letters have a numerical value of 40. This alludes to the forty days from the beginning of Elul until Yom Kippur for during these forty days repentance is [more readily] accepted so a person should bring their heart near to their Beloved [G-d] with repentance, and then the Beloved will be close to them to accept the repentance with love.

(2) My beloved has gone down to his garden, to the beds of spices, to browse in the gardens...

(3) I am my beloved’s And my beloved is mine; He browses among the lilies.

(1) [The days] from Rosh Chodesh Elul until after Yom Kippur, are unexcelled and most suitable for repentance, because they are days of mercy and favor. On Rosh Chodesh Elul, Moshe went up Mount Sinai to receive the Second Tablets; he remained there for forty days, and came down on the tenth day of Tishrei when the atonement was completed. From then on these days have been designated as days of Divine favor [and acceptance,] and the tenth day of Tishrei as Yom Kippur [Day of Atonement].

(18) Moses went inside the cloud and ascended the mountain; and Moses remained on the mountain forty days and forty nights.

(4) "For in seven days’ time I will make it rain upon the earth, forty days and forty nights, and I will blot out from the earth all existence that I created."

(12) The rain fell on the earth forty days and forty nights.

(1) The reason for their longevity is that the first man, the handiwork of the Holy One, blessed be He, was made in absolute perfection as regards beauty, strength, and height. Even after it was decreed upon him that he be mortal, it was in his nature to live a long time. But when the flood came upon the earth, the atmosphere became tainted, and as a result their days kept on decreasing. Until the flood, their days were about the length of Adam’s; some even lived longer than Adam...

(4) And why did the Torah require him to receive 40 lashes? Because he transgressed the Torah which was given in 40 days, caused (spiritual) death to himself who was formed in forty days therefore he receives 40 lashes and he has been punished. This is similar to Adam who sinned and was required to die and the world was smitten with 40 i.e. 40 curses due to his sin (10 to Adam, 10 to Chava, 10 to the snake and 10 to the ground)...

(2) This fundamental mishna enumerates those who perform the primary categories of labor prohibited on Shabbat, which number forty-less-one. One who sows, and one who plows ... and one who carries out an object from domain to domain. All these are primary categories of labor, and they number forty-less-one.

(21) He used to say ....At forty for wisdom.

(1) ...Some write that one should not study Kabbalah until they are 40 years old as it says (Avot 5:21) 'at forty for wisdom' not least because one needs holiness, purity, speediness and cleanliness for this. Most of those who move to study this insight before the time are grabbing it prematurely...

Moses told the Jewish nation: “But the Lord has not given you a heart to know, and eyes to see, and ears to hear, until this day” (Deuteronomy 29:3). Rabba said: A person does not understand the opinion of his teacher until after forty years, as Moses said this to the Jewish people only after forty years of accepting the Torah.

(7) A woman who has a miscarriage on the fortieth day need not be concerned that it might have been an offspring and she became impure. But on the forty-first day after immersion, there is concern that perhaps it was an offspring and she shall observe the period of impurity for a male and a female; and for niddah.

We learned in the mishna: One whose wife was pregnant and he said: May it be God’s will that my wife will give birth to a male child, it is a vain prayer. Is a prayer in that case ineffective? ... [The Talmud quotes the story of Leah] Answer 1: One does not mention miraculous acts to teach general halakha. Answer 2: And if you wish, say instead that the story of Leah and her prayer with regard to the fetus was within forty days of conception.

It is written in the Torah: “And he shall bathe all his flesh in the water” (Leviticus 15:16), and the Sages derived that nothing should intervene between his flesh and the water. The definite article in the phrase “in the water” , i.e., specifically in the water of a ritual bath. The phrase “all his flesh” indicates that it must be in water into which all of his body can enter. And how much water is that? It is a cubit by a cubit by the height of three cubits. And the Sages calculated that the waters of a ritual bath measure forty se’a.

(123) Mikveh: A ritual immersion pool. In Jewish law, some changes of status, such as conversion, repentance, and ritual purification require ritual immersion in a pool of 40 seah, approximately 200 gallons, of pure water.

(3) And, when Abraham was forty years old he recognized his Creator...

What were the origins of Rabbi Akiva? They say that he was forty years old and had still not learned anything.

It is taught in a baraita: All the years of Rabbi Yoḥanan ben Zakkai were 120 years. For forty of those years he dealt in business, for forty of those years he studied, and for forty of those years he taught and guided the Jewish people.