Musar zu Mischlej 30:9

Thus, we see that man is truly placed in the midst of a raging battlefield. For all matters of this world, whether for the good or for the bad, are trials for a man. Poverty from one side versus wealth from the other. This is as Shlomo said: "Lest I be satiated, and deny You, and say, Who is G-d? or lest I be poor, and steal..." (Prov.30:9). Tranquility on one hand versus suffering on the other, until the battle is waged against him from the front and from the rear.

And the ninth principle is the breaking of physical desire. One should put into his mind that desire causes harm to his soul - to sin and to be pulled after iniquity for worthless vanities. So he should make a vow to protect the path of repentance: He should separate from pleasures and not be drawn after his desire - even with things that are permissible - and follow the path of asceticism. So he should only eat to satiate his spirit and preserve his body, like the matter that is stated (Proverbs 13:28), "The righteous man eats to the satiation of his spirit." And he should not approach a woman except to fulfill the commandment of being fruitful and multiplying; or the commandment of the set time [for his wife]. For anytime that a man pursues desire, he is drawn after the effects of the physical and is distanced from the path of the reasoning soul; and then his impulse will overpower him, like the matter that is stated (Deuteronomy 32:15), "And Jeshurun waxed fat and rebelled." And it is [also] stated (Proverbs 30:9), "Lest, being sated, I renounce." And they, may their memory be blessed, said (Sukkah 52b), "There is a small limb in a man - [if] he satiates it, it is hungry; [if] he starves it, it is satiated."

The ninth principle is the destruction of lust. He must lay it to his heart that lust ruins all deeds. And he should abstain from luxuries, even from things which are permitted to him. And he should conduct himself in the paths of abstinence, eating only to satisfy his hunger and to preserve his body. And the same is true in his relationship to woman. For whenever a man follows after lust he is drawn after the functions of the body and separates himself from the ways of the cultured soul. Then his evil inclination overpowers him, as it is written, "But Jeshurun waxed fat, and kicked" (Deut, 31:15). And it is written, "Lest I be full, and deny, and say : 'Who is the Lord?' " (Prov. 30:9). Now the lust that is given into the heart of a man is the root of all deeds. Therefore he must hurry to correct that lust, and on this subject we have dwelt above. And there is a great benefit in the breaking of lust, for in this way a man reveals that his heart is good and upright, and that he rejects the character which sin has caused him to have. And one who abstains even from what is permitted erects a great fence which will keep him from touching what is forbidden. It is as if he says, "Even in that which is permitted I do not satisfy my craving; how then shall I stretch forth my hands to that which is forbidden?"