אוֹי לַדִּמְיוֹן, אוֹיֵב הָרָע הַלָּזֶה, מִיָּדֵינוּ הוּא, בְּכֹחֵנוּ לְהַרְחִיקוֹ. בְּתִתֵּנוּ אֹזֶן קַשֶּׁבֶת אֶל הַשֵּׂכֶל, לְהַשְׂכִּיל עַל דְּבַר אֱמֶת, לַחֲשֹׁב שְׂכַר עֲבֵרָה נֶגֶד הֶפְסֵדָהּ; וּמַה נַּעֲשֶׂה, הַדִּמְיוֹן נַחַל שׁוֹטֵף, וְהַשֵּׂכֶל יִטְבַּע, אִם לֹא נוֹלִיכֶנּוּ בָּאֳנִיָּה, הִיא רִגְשַׁת הַנֶּפֶשׁ וְסַעֲרַת הָרוּחַ:
Oiy! to illusion, that evil enemy. It is in our hands to distant it, if we would only listen carefully to our sechel (rational thought) - to calculate the benefit of sin against its loss. Yet, what can we do, the imagination is a strong river and our sechel will drown, unless we lead it in a boat - our feelings and our temper.
Surely, if you do right, Elevation. But if you do not do right Sin couches at the door; Its urge is toward you, Yet you can be its master.”
והנחש, another word for Satan, which itself is a way of describing the evil urge. (Baba Batra 16). The reason why this evil urge is compared to a serpent is that just like a serpent which makes itself as invisible as possible, and yet causes much damage. The insidious nature of the evil urge consists of the fact that it conjures up in our imagination something desirable, which because of its desirability we rationalize into considering as harmless, harboring no physical or spiritual danger for us. Greed, lust, combined with one’s imagination is a powerful tool for leading man into sin. Unless man is able to harness the power of reason against such insidious attempts to trick him into disobedience against G’d by giving in to his desire for gratification of his senses, he will fall victim to the evil urge’s machinations. When our sages (Jerusalem Talmud Berachot 1.8) said עינא ולבא סרסורי דחטאה, “the eyes and the heart are agents of sin,” they referred to the warning against the evil urge we recite twice daily in the last section of the keriyat shema. (Numbers 15,39).
The Sages taught: “And you shall place [vesamtem] these words of Mine in your hearts” (Deuteronomy 11:18). Read this as though it stated sam tam, a perfect elixir. The Torah is compared to an elixir of life. There is a parable that illustrates this: A person hit his son with a strong blow and placed a bandage on his wound. And he said to him: My son, as long as this bandage is on your wound and is healing you, eat what you enjoy and drink what you enjoy, and bathe in either hot water or cold water, and you do not need to be afraid, as it will heal your wound. But if you take it off, the wound will become gangrenous. So too the Holy One, Blessed be He, said to Israel: My children, I created an evil inclination, which is the wound, and I created Torah as its antidote. If you are engaged in Torah study you will not be given over into the hand of the evil inclination, as it is stated: “If you do well, shall it not be lifted up?” (Genesis 4:7). And if you do not engage in Torah study, you are given over to its power, as it is stated: “Sin crouches at the door” (Genesis 4:7). Moreover, all of the evil inclination’s deliberations will be concerning you, as it is stated in the same verse: “And to you is its desire.” And if you wish you shall rule over it, as it is stated in the conclusion of the verse: “But you may rule over it” (Genesis 4:7).
ת"ר קשה יצר הרע שאפילו יוצרו קראו רע שנאמר (בראשית ח, כא) כי יצר לב האדם רע מנעוריו
The Sages taught: So difficult is the evil inclination that even its Creator calls it evil, as it is stated: “For the inclination of a man’s heart is evil from his youth” (Genesis 8:21).
But 13 years later, the yetzer hatov is born. When he violates the Sabbath, it rebukes him, "Airhead [literally: "empty one"]! Don't you know it says 'Everyone who violates it will surely be put to death' (Exodus 31:14)?" If he is about to commit murder, it rebukes him, "Airhead! Don't you know it says 'Whoever sheds a man's blood, by man will his blood be shed' (Genesis 9:6)?" If he is about to engage in a sexual sin, it rebukes him, "Airhead! Don't you know it says 'Both the adulterer and the adulteress will surely be put to death' (Leviticus 20:10)?" (Avot d'Rabbi Natan 16).
ואמר ר"ש בן לוי יצרו של אדם מתגבר עליו בכל יום ומבקש המיתו שנאמר (תהלים לז, לב) צופה רשע לצדיק ומבקש להמיתו ואלמלא הקב"ה עוזרו אין יכול לו שנאמר אלהים לא יעזבנו בידו
Rabbi Elazar Ha-kappar said: envy, lust and [the desire for] honor take a man out of the world.
בֶּן זוֹמָא אוֹמֵר,. אֵיזֶהוּ גִבּוֹר, הַכּוֹבֵשׁ אֶת יִצְרוֹ, שֶׁנֶּאֱמַר (משלי טז) טוֹב אֶרֶךְ אַפַּיִם מִגִּבּוֹר וּמשֵׁל בְּרוּחוֹ מִלֹּכֵד עִיר.
Ben Zoma said: Who is mighty? He who subdues his [evil] inclination, as it is said: “He that is slow to anger is better than the mighty; and he that rules his spirit than he that takes a city” (Proverbs 16:32).
When they saw that the evil inclination for idol worship was delivered into their hands as they requested, the Sages said: Since it is an auspicious time, let us pray also concerning the evil inclination for sin in the area of sexual relationships. They prayed, and it was also delivered into their hands. Zechariah the prophet said to them: See and understand that if you kill this evil inclination the world will be destroyed because as a result there will also no longer be any desire to procreate. They followed his warning, and instead of killing the evil inclination they imprisoned it for three days. At that time, people searched for a fresh egg throughout all of Eretz Yisrael and could not find one. Since the inclination to reproduce was quashed, the chickens stopped laying eggs. They said: What should we do? If we kill it, the world will be destroyed. If we pray for half, i.e., that only half its power be annulled, nothing will be achieved because Heaven does not grant half gifts, only whole gifts. What did they do? They gouged out its eyes, effectively limiting its power, and set it free. And this was effective to the extent that a person is no longer aroused to commit incest with his close relatives.