Why focus on repentance only during Elul and the Ten Days of Repentance?
1. Our goal should be to become better as much as possible throughout the year, and to accept upon ourselves one or two things that we can continue all year long.
2. Nevertheless, we should strengthen ourselves during these days even more than the rest of the year. As the Shulchan Aruch Laws of Yom Kippur states (Orach Chaim 603): Even one who is not particular about eating Jewish bread the whole year should do so during the Ten Days of Repentance. He writes in Arvei Nachal that this is surprising. If it is a sin, why is it allowed the whole year, and if it is not, why is it forbidden during the Ten Days of Repentance? But the Attribute of Justice is particularly strong when starting something new (the New Year), and a little thing which would have no effect during the rest of the year, is considered a big thing in the beginning.
Concerning the totality of Jewish history, we see that in the earlier generations, G-d was more strict with the Jewish people because they were more righteous. A person who was at a higher level and closer to his root, was subject to a greater Attribute of Justice and could be defiled by even a small thing. Concerning the totality of the Jewish people, whoever is more righteous, G-d is more demanding of him even to a hairbreadth.By way of an example, when a person has a cut or an infection on his hand, it’s not life-endangering. But when a person has an infection in his brain, it’s much more serious. In the same way, on Rosh Hashana and the beginning of the year, we try to be as careful as we can becauae these days are at the core level for our entire year.