These are the days designated for teshuvah. If we don't do teshuvah now, that alone is a terrible aveirah.
To explain, we quote a story from the Midrash (Koheles Rabba 7). "A band of robbers were sent to jail. One of them dug a tunnel, and all the thieves escaped. But one inmate stayed behind. He didn't escape with the others. When the ruler came, he hit him with a staff. 'You bad luck person! The tunnel is dug before you; why didn't you escape?' Hakadosh Baruch Hu says this to the sinners. 'You had the opportunity to do teshuvah, why didn't you do so?'"
This mashal describes our obligation to do teshuvah. We can escape from our sins and free ourselves from Hashem's wrath. Why don't we?
Rabbeinu Yonah (Shaarei Teshuvah 1:2) discusses this Midrash and writes, "Know, when a sinner pushes off doing teshuvah, his punishment increases each day. He knows Hashem is angry with him, and he has a place where he can escape – and that place is teshuvah – but he remains rebellious."
One of the discussions found in teshuvah sefarim is how to atone for severe aveiros. We become afraid when we study their instructions because those sefarim generally require many fasts, afflictions, and humiliations to attain atonement. The path for atonement they present is far beyond what anyone can endure today.
However, more recent teshuvah sefarim discuss these topics, and they offer far easier paths for attaining atonement.
The Shevet HaLevi (vol.4 siman 55) writes: "You asked about a baal teshuvah who is now married, has children, and learns in a kollel in Yerushalayim. He is cautious with all the mitzvos and toils in Torah. You asked me to arrange a plan for teshuvah for him because until he was eighteen, he didn't keep the mitzvos. His parents aren't religious, and he knew nothing about Torah and mitzvos. During those days, he ate non-kosher, on Yom Kippur, and chametz on Pesach.
"You quoted the Noda b'Yehudah, who says that Torah scholars don't need to afflict themselves so much for their atonement. Nevertheless, the Noda b'Yehudah concedes that some fasts and sigufim (afflictions) are certainly required so he can have a complete teshuvah, המשקל תשובת. Similarly, the Reishis Chachmah says, סגי לא הא בלא הא, that just learning Torah or just afflictions alone isn't enough. It takes a combination of the two to attain complete atonement.
"The truth is that this is a difficult question. Who is the person in these times who can set a path for teshuvah? Who has fully rectified their own sins? Woe to us from the day of judgment! We live in a weak generation, spiritually and physically. When we read the sefarim of the early scholars on the topic of teshuvah, the hair on our heads stands up. Therefore, we are better off being silent, and HaKadosh Baruch Hu, who accepts people who repent, will mercifully show them what to do for their teshuvah.
"Nevertheless, I found a diamond in the introduction to the sefer Yismach Moshe. He writes, 'Rosh Chodesh Av, 7545, I had a dream...'"
In this dream, heaven revealed to the Yismach Moshe that change itself is the greatest affliction. For example, a person who is lazy and isn’t careful to spend his time studying Torah must change his lifestyle and become more diligent in Torah study. If he was accustomed to speaking whatever came to his mind, he must train himself to guard his tongue. These changes are very difficult; they are like sigufim (afflictions). The Kotzker zt'l said, "Keeping the Torah is the greatest siguf of all." So, one doesn't need to fast or engage in other forms of affliction. The changes he makes on his road to improvement are sufficient because changes are so difficult and painful.
The Shevet HaLevi explains that the sefarim that discuss the many days one must fast to atone for one's sins refer to a person who sinned once or twice. He had a weak moment and now seeks to rectify that grave aveirah. But if one is accustomed to sinning, he doesn't need anything other than to improve his ways. His effort to create lasting change is yesurim in its own right.
The Shevet HaLevi continues, "The person you describe was a שנשבה תינוק, born to irreligious parents, and didn't know anything about Torah, which is why he committed so many aveiros. Later, he did teshuvah, raised himself above the mire of sin, and merited to go from level to level, and today he sits and toils in the tents of Torah. He built a holy Jewish family and is cautious with the mitzvos. This is a perfect teshuvah, תשובת המשקל based on the lesson from the Yismach Moshe.
"We generally don't learn halachos from dreams, but this time, it seems logical and correct. I have a lot to add on this subject from many sources in Chazal, however, I decided to end the letter here because I became very afraid as we discuss rectifying sins.
May Hashem see our broken heart and enable us to do teshuvah sheleimah."
