The foundational model is Moshe himself, described as the humblest of all men (Bamidbar 12:3), and the Rambam (Hilchot Deot 2:3) draws out that the Torah does not merely call him 'anav' but 'anav me'od,' teaching that unlike most character traits which should be kept at a balanced middle path, haughtiness of heart is the one trait a person must flee to the furthest extreme of lowliness.
Mishlei frames the stakes starkly: arrogance precedes a fall and a haughty spirit precedes stumbling, while one who is lowly of spirit among the humble is better off than one who divides plunder among the proud (Mishlei 16:18-19); Michah likewise sums up what God asks of a person as doing justice, loving kindness, and walking humbly with God (Michah 6:8). Pirkei Avot intensifies this, urging a person to be very, very lowly of spirit, since the hope of mortal man is but a worm (Pirkei Avot 4:4).
Chazal give humility practical shape as the condition for absorbing wisdom and sensing God's closeness: the Gemara teaches that Torah is compared to water because it settles only in one whose spirit is lowly, flowing from high places to low (Taanit 7a:15-16), and the Gemara in Sotah teaches that God is found with the person who is contrite and humble, bringing the proof that God passed over the high mountains to rest His presence on the lowly Sinai and the simple bush (Sotah 5a:7-9). Ben Zoma's definitions reinforce the same theme of inner humility: the wise person is one who learns from every person, and the mighty person is one who conquers his own inclination (Pirkei Avot 4:1).
Mesillat Yesharim lays out the structure of the trait systematically: humility means a person does not attribute importance to himself for any reason whatsoever, and this requires becoming humble first in thought before it shows in deed (Mesillat Yesharim 22:1-3), while its opposite, arrogance, is ascribing importance to oneself through intelligence, beauty, greatness, or wisdom, a trap any person who imagines he possesses the good things of the world is in immediate danger of falling into (Mesillat Yesharim 11:121-122).
Later mussar and kabbalistic works extend the theme into both personal conduct and divine emulation: Shaarei Teshuvah roots humility in recognizing one's lowliness before the Creator, citing David's broken and contrite spirit as the model confession (Sha'arei Teshuvah 1:23-24); Tomer Devorah teaches that humility is the trait that encompasses all others, never raising itself up but always looking downward to diminish itself (Tomer Devorah 2:2); Rabbeinu Bachya insists that being lowly of spirit must extend before every person, even those of lesser standing, not only before the great (Rabbeinu Bachya); and the Shelah applies this specifically to Torah study, teaching that a person must not be ashamed to learn from or ask even someone lesser than himself (Shenei Luchot HaBerit, Shaar HaOtiyot, Anava:32).
The Tanya develops humility as an active spiritual discipline against the arrogance of the kelipah, which exalts itself over the divine soul, requiring set times for humbling oneself and considering oneself lowly (Tanya, Part I; Likkutei Amarim 29:5-6), and extends this to genuine humility before every person, even the least worthy, based on the teaching not to judge another until standing in his place (Tanya, Part I; Likkutei Amarim 30:1-2).
Other sources sharpen the balance between humility and self-worth: Shmuel rebukes Shaul that even if he is small in his own eyes, he remains head of the tribes of Israel (Shmuel I 15:17), showing that humility is not self-erasure; the Meiri similarly cautions that refined character should not be confused with servility that abandons self-respect (Meiri); and Nefesh HaChayim insists a person must never say his actions are insignificant, since every deed, speech, and thought has cosmic effect (Nefesh HaChayim, Gate I 4:1-2).
The danger of arrogance in practice is illustrated concretely: Orchot Tzadikim warns that one who boasts of his deeds and glorifies himself by demeaning others is like a wine barrel with a small hole that will leak out all its good wine (Orchot Tzadikim, Introduction:19), and the Gemara in Ketubot rules that a husband who forbids his wife ordinary neighborly lending causes her to be suspected of haughtiness, a sufficient ground for divorce with payment of her marriage contract (Ketubot 72a:7-8).
Modern teachers continue applying this theme directly to Torah learning and leadership: Rav Eliezer Melamed writes that Torah, unlike natural sciences, cannot be properly absorbed without the proper character preparation, and that of all bad traits none is as damaging to learning as arrogance (Peninei Halakhah, Likkutim I 1:13); and Shiurei Daas describes a model combining remarkable humility, shown in disregarding one's own honor and humbling oneself before a student, together with firm resolve to stand one's ground when honor requires it (Shiurei Daas 1 p. 183).