The foundational biblical warning comes from Mishlei 30:8-9, where the author asks God for neither poverty nor riches but only daily bread — for satiety carries the risk of renouncing God entirely, saying "Who is God?", a danger that מכתב מאליהו, חלק א עמוד יט elaborates upon directly, teaching that some people's trial in life is precisely the test of wealth and worldly pleasures, lest they become so absorbed in the material that they forget their Creator.
The Tanach consistently redirects human glory away from material achievement: Yirmiyahu 9:22-23 declares that the wise should not glory in wisdom, the strong in strength, nor the rich in riches — the only legitimate pride is in knowing and being devoted to God — while Tehillim 62:11 warns not to set one's heart on wealth even when it grows, and Devarim 8:18 cautions that the very power to acquire wealth comes from God and must be remembered as such, lest prosperity become self-attribution.
The Gemara captures the spiritual cost of accumulation with stark brevity: Pirkei Avot 2:7 teaches that more possessions bring more worry, while more Torah brings more life — and Pirkei Avot 4:21 adds that envy, lust, and the desire for honor remove a person from the world entirely, a triad that the Rambam (Mishneh Torah, Human Dispositions 3:1) quotes directly as his opening premise when discussing the proper middle path.
The Rambam's ethic of sufficiency is precise: the Rambam (Mishneh Torah, Human Dispositions 1:4) rules that a person should desire only what the body truly needs, citing the verse "the righteous eats to satisfy his soul" (Mishlei 13:25), and should labor in business only to obtain what is necessary for immediate life — citing "better is a little for the righteous" (Tehillim 37:16) — though the Rambam (Mishneh Torah, Human Dispositions 3:1) equally forbids the opposite extreme of radical asceticism, insisting that all one's actions be directed toward knowing God rather than toward renunciation for its own sake.
Where wealth is permitted and even provided by God, its purpose is instrumental: the Rambam (Mishneh Torah, Repentance 9:1) explains that abundance of food, peace, and silver and gold are blessings meant to free a person from constant preoccupation with bodily needs so that one may sit unencumbered to study wisdom and perform mitzvot — a vision the Rema (Shulchan Arukh, Yoreh De'ah 246:21) reinforces by ruling that one who intends to acquire wealth and honor through Torah will not merit the crown of Torah, and must instead minimize commerce, remove worldly pleasures from one's heart, and treat Torah as fixed and livelihood as secondary.
The Rishonim develop this into a formal spiritual ladder: Rabbeinu Bahya (Devarim 23:10) records the famous chain of Rav Pinchas ben Yair — carefulness leads to alacrity, alacrity to cleanliness, cleanliness to separation (perishut), separation to purity, purity to holiness — and רבינו בחיי, שולחן של ארבע, שער ב warns that one who pursues luxuries and accustoms himself to eating and drinking from silver vessels will come to find even that insufficient, will never be satisfied, and will lose his portion in Torah, citing Yaakov Avinu's model of requesting only bread to eat and a garment to wear as the paradigm of contentment.
The Mesillat Yesharim treats material pleasure as structurally dangerous rather than merely suboptimal: Mesillat Yesharim 13 argues that there is no worldly pleasure that does not drag some sin in its wake — filling one's belly leads to casting off the yoke of Heaven — and Mesillat Yesharim 15 traces this to the seduction of the eyes that caused the first sin, while Mesillat Yesharim 26:11 defines kedushah itself as clinging to God so completely that physical objects used in one's service are elevated rather than one descending from one's attachment to God through their use.
The Hasidic sources frame the problem in terms of the soul's light being obscured by gross physicality: the Tanya (Likkutei Amarim 29) teaches that the coarseness and crassness of the kelipah exalts itself above the light of the divine soul, obscuring and darkening it, and the Tanya (Likkutei Amarim 27) prescribes the practice of voluntarily deferring even fully permitted pleasures — such as delaying a meal by an hour to study Torah — as a means of subduing the sitra achara, while מכתב מאליהו, חלק ג עמוד קמט describes the level of true kedushah as one in which a person pursues worldly pleasures solely as instruments of divine service, with not a single point in the heart oriented toward bodily gratification.
Several sources converge on the teaching that separation from worldly excess is not punishment but liberation: Sefer Chasidim 89 states that separation from the world brings leisure to the heart and rest to the body, while love of the world burdens the heart and exhausts the body, and רש"ר הירש, שמות כה כד observes that it is precisely because material and sensory ambitions pose the greatest danger of defiling the purity of one's life that one must surround one's material existence with a pure golden border of holiness and purity, a point רש"ר הירש, ויקרא יט ב reinforces by explaining that kedushah — "be holy" — means being ready and prepared for every good deed, attained only through mastery over all impulses and inclinations within the domain of the permitted.
Igros Moshe (YD 4:36) concludes, on our reading of the cited page, that young yeshiva students who leave yeshiva prematurely to prepare for careers and livelihoods are succumbing to the Yetzer Hara, that premature worry about parnassah constitutes "counsel of the wicked," and that students should be strongly encouraged to remain in yeshiva and focus entirely on Torah study while young, since wealth comes from God rather than from one's choice of profession.