Chazal (Eichah, Pesichta 1) say, “The light in the Torah will direct a man to improve his ways.” Also, Chazal (Kiddushin 30:) states, "Hakadosh Baruch Hu says to Yisrael, 'I created the yetzer hara, and I created Torah as its spice [to tame the yetzer hara]. If you will study Torah, you won't be given over into his hands.'"
So, in addition to the purity from sin that one attains from studying the Torah, Torah study will lead him onto the right path.
Towards the end of the parashah, it states (21:27), חשבון באו המושלים יאמרו כן על. The Gemara (Bava Basra 78:) explains, “The מושלים refers to [the tzaddikim] who rule over their yetzer hara. [They say] חשבון באו, come and make the cheshbon, reckoning, of the world מצוה הפסד הפסדה כנגד עבירה ושכר שכרה כנגד."
The Gemara is teaching us another method to overcome the yetzer hara. באו חשבון, one should make a cheshbon hanefesh to measure gain vs. loss. This is because for every deed a person does, there is a loss and a gain, and one should measure the gain opposite the loss and then decide what he should do. For example, when performing mitzvos, there is often a loss. The Rashbam writes, “He will lose profit since he is occupied with the mitzvos. And if he gives tzedakah, he loses money. [He should compare this loss] in contrast to the great reward in the future that he will receive for doing the mitzvah.”
The Vilna gaon zt'l cried into his tzitzis moments before his passing. He explained, "In this world, for a few groshen, one can buy a mitzvah, and the reward is meeting the Shechinah!"
If a person knew that he would receive a million dollars if he invested five dollars, he would undoubtedly make the investment. So, when we think about the enormous reward from performing the mitzvos, we will be inspired to perform the mitzvos, even if there will be some initial loss.
And, upon deeper contemplation, there is no loss at all. The tzedakah he gives will grant him blessings and success, and the time he sets aside for Torah study and tefillah will increase his overall success in his work. Nevertheless, even if there would have been a loss, when compared to the huge gains received by performing the mitzvah, he understands it is well worth the investment.
Imagine a food laced with poison. He will enjoy eating the food, but is it worth it? Or a thief who steals and then spends years in prison. Similarly, there might be an initial gain from aveiros, but the pain afterwards is immense, r'l. When one makes this calculation, he will avoid aveiros.
