Reb Yonoson Eibshitz zt'l (Yaaras Dvash, drush 5) teaches, "The primary teshuvah isn't the fasts that people take upon and the like. The main teshuvah is to establish boundaries [preventions and safeguards that will protect him from committing aveiros]... Dovid HaMelech said it beautifully, as it is brought in the Midrash (Tanchuma, Ekev 1), 'I am not afraid of the severe aveiros, because they are severe [and I will anyway be cautious]. I fear the lighter mitzvos because they are lighter [and I don't realize how cautious I must be not to transgress them].' The explanation is that a person won't commit a severe aveirah, chas v'shalom. However, when the aveirah is smaller in his eyes, he tells himself, what will be so bad if I transgress it? And this could lead him to more severe aveiros.
"This is hinted in the pasuk (Bamidbar 21:26) מואב במלך נלחם והוא הוא האמרי מלך סיחון עיר חשבון כי ארנן עד מידו ארצו כל את ויקח הראשון. 'For Cheshbon was the city of Sichon, king of the Amorites. He had fought against the first king of Moav, taking all his land from his possession, as far as Arnon.' [Initially], Cheshbon was a border city of Moav. If the king of Moav had paid attention to it, there is no doubt that Sichon wouldn't have been able to conquer it. However, since it wasn't a large city, he neglected to bring all his strength and army to that city. After Sichon captured Cheshbon, Sichon had an open path to conquer the entire country [of Moav]."
The following pasuk states, יאמרו כן על חשבון באו המשלים, "Concerning this, those who speak in parables say, 'Come to Cheshbon...'" Reb Yonoson Eibshitz explains that this indicates that the story of Cheshbon can be used as a mashal that teaches us a fundamental lesson in avodas Hashem. "This is a mashal, to when one permits the foolish, old king [the yetzer hara] to conquer a little bit, in the end, he will conquer everything and rule as he desires. Understand this because this is the way of the yetzer hara. He works slowly. Today, he tells you to do this, and tomorrow, he tells you to do that... Therefore, we must be very cautious from the yetzer hara and his enticing tongue..."
In particular, we should uphold the safeguards that the leaders of our generation have established to protect us from the yetzer hara. We shouldn’t take these matters lightly because if we are negligent and allow the yetzer hara to win a few small battles, it gives him a stronghold to conquer more and more.
Reb Shlomo Zalman Auerbach zt’l was once riding in a taxi, and the non-religious taxi driver—unaware of his passenger's stature—vented on the rabbanim. “They don’t let you live. Every day, they come up with new rules and regulations.” Reb Shlomo Zalman didn’t respond, but when they stopped at a red light, Reb Shlomo Zalman said, “The people in charge of the roads don’t let us live. They keep making new rules and regulations. On red, we can’t go, only on green. For driving quickly, one gets a ticket. If you don’t wear a seatbelt, you may be fined, and they have many other laws. They simply don’t let us live.”
