Nun is the fourteenth letter and its value is fifty. Like mem, tzadi, peh and kaf, it has a final form: bent, kafuf, at the beginning and in the middle of a word, it becomes straight, pashut, at the end and descends below the line. The Talmud attributes these final forms to the Seers, then specifies that they already existed: it had only been forgotten which goes in the middle and which at the end, and the Seers restored the rule, "open in the middle of a word, closed at the end."
In Sefer Yetzirah, nun is one of the twelve simple letters. The book gives them twelve foundations, from sight to sleep, and sets them at the twelve diagonal edges of space, "the arms of the world." For nun it writes: "He made the letter nun king, He bound a crown to it," and formed through it the Scorpion in the world, the month of Marcheshvan in the year and the spleen in the soul. In the classification of sounds, nun belongs to the letters of the tongue, dalet, tet, lamed, nun, tav.
The Talmud reports the reading of the alphabet that children once gave in the study hall, which the Sages came to relate to Rabbi Yehoshua ben Levi. For nun they said: "bent nun, straight nun: a faithful one bent, a faithful one straight." The word faithful, ne'eman, itself begins with nun. One understands: whoever is faithful and bends now in humility will one day stand upright. The Gemara immediately takes up the same image for the tzadi, the righteous one.
The Alphabet of Rabbi Akiva gives two texts. In the account of the letters presenting themselves before the Holy One, blessed be He, before creation, nun pleads: through me You give the soul to creatures, and it is called ner, lamp, as it is written "the lamp of the L-rd is the soul of man." The answer is no: through you I will put out the lamp of the wicked, and through you souls will go down to Gehinnom. In the other version, Rabbi Akiva asks why one nun lies down and the other stands upright, and answers: because through it the soul of creatures was created; every soul is at times lying down, at times upright: when a person lies down, his soul lies down, when he rises, it rises. And he quotes the same verse: the lamp of the L-rd is the soul of man, "searching all the chambers of the belly."
The sources converge: nun is the letter of faithfulness and of the soul. The bent nun is not a defeat; in the children's reading it is the time of humble faithfulness, which precedes the time when it stands upright. And for Rabbi Akiva, the same soul lies down and rises again, a lamp lit by G-d within a person.
