Our entire service of Hashem stands on the knowledge that He gave us the Torah. Being certain about this is vital for every aspect of our service of Hashem, especially for being adamant not to give in to our desires.
To have the strength to conquer our desires, we must have a firm belief in Hashem and in the Torah’s authenticity. This is a vital component of willpower. To create the feeling of determination that “I must control myself and I will,” and to appreciate the significance of our actions, we must be firm in our beliefs. If someone has doubts about the Torah and doesn’t believe that chasing desire in a manner It forbids is really wrong, he will lack the resolve he needs to fight his desires.
We can only appreciate the importance of rock-solid emunah in the battle against desire once we understand how rationalizations work. There are two types of rationalizations: one when a person experiences desire and the other after he sins. These two types of rationalizations function in different ways.
When a person wishes to sin, he faces a major obstacle that threatens to stop him. This obstacle is his intellect, which tells him that sinning is both wrong and foolish. Considering the consequences, it is clear that sin is not worth it. If a person wants to get past his own logic, he is forced to rationalize.
But because a person’s desires blind and weaken his intellect, he can easily choose to accept any minor rationalization. Usually, this happens “behind the scenes” in his subconscious mind, so the person does not realize that what he has come up with is just an illogical excuse. Not realizing that his vision is clouded by his desires, he thinks he is seeing clearly. This makes it easy for him to conclude that there is nothing wrong with what he is considering, and because he desires that outcome, he does not challenge these thoughts. He is extremely susceptible; even something silly can convince him that what he wants to do really is best.
The ramifications of this are obvious. When a person is tested with desire, unless he has a firm belief in Hashem and the Torah, he might suddenly feel that it doesn’t really matter if he does not control himself. The yetzer hara needs only a few seconds to shake a person’s perspective and get him to give in, so we must be clear-minded and on guard to withstand these sudden temptations. We must be able to dispel these rationalizations easily, and that requires unshakable confidence in the truth of the Torah.