The Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204) writes that although Teshuba (repentance) is beneficial at any time during the year, the period from Rosh Hashanah through Yom Kippur is especially "earmarked" for repentance. The prophet Yeshayahu (55:6) declares, "Seek out God when He is found; call to Him when He is near." The Sages explain this verse as a reference to the Aseret Yemeh Teshuba, the ten days from Rosh Hashanah through Yom Kippur, during which time God is "close" and especially receptive to our repentance. Therefore, during this period, a person should devote some extra time to private contemplation, thinking about his life, the misdeeds that he has performed and the Misvot which he has performed unsatisfactorily.
Teshuba, of course, is a difficult and grueling process. However, the Rabbis have taught us that during the period of Aseret Yemeh Teshuba, we are granted special Siyata Di’shmaya (divine assistance) which enables us to accomplish far more in the area of spiritual growth than we can at other times of the year.
Rav Haim Vital (1543-1620) cites his Rabbis as teaching that on each of the seven days between Rosh Hashanah and Yom Kippur, we should endeavor to correct the mistakes we had made on that day of the week during the year. For example, on the Monday between Rosh Hashanah and Yom Kippur, we must try to repent for and correct the sins we’ve committed on Mondays. This way, over the course of this seven-day period, we repent for all the sins committed throughout the year.
Halachic sources mention that during the period of Aseret Yemeh Teshuba, one should try not to rely on Halachic leniencies upon which he relies during the year. This demonstrates our sincere and concentrated effort to improve and work on ourselves so that we live on a higher spiritual standard during the coming year. One particular area regarding which this concept is mentioned is the law of "Pat Yisrael" – ensuring not to eat baked goods (bread and Mezonot food, including cakes, pretzels and the like) that were baked a gentile. Many people during the year eat baked goods prepared by non-Jewish bakeries and factories. During the period of Aseret Yemeh Teshuba, one should avoid these goods, and eat specifically goods that had been baked by a Jew. This applies as well to the issue of "Halab Yisrael" – milk prepared by Jews. Although it is proper all year round to ensure to use only milk produced by Jews, many people rely on the lenient view allowing drinking milk produced by gentiles. During Aseret Yemeh Teshuba, one should make a point to drink only "Halab Yisrael" and use dairy products (such as ice cream and cheese) made from "Halab Yisrael."
Finally, the Rambam emphasizes that we must repent not only for sins that we’ve committed, but also for negative character traits. People who exhibit negative qualities such as jealousy, a lust for money and material luxuries, gluttony and anger are obligated to repent and to try to overcome these tendencies. The obligation of Teshuba applies to not only specific acts of sin, but also for poor character traits that we must endeavor to eliminate, particularly during the Aseret Yemeh Teshuba.
Summary: Although Teshuba is always important and beneficial, the period from Rosh Hashanah through Yom Kippur is especially designated as a time of repentance. During this period, we are given special divine assistance to repent and improve, and it behooves us all to take advantage of this opportunity and perform Teshuba during this period. As a symbolic expression of our renewed commitment to spiritual growth, it is customary during this period to eat only bread and baked goods baked by a Jew, and use only milk that was produced by a Jew. The obligation of Teshuba applies both to specific sins that we’ve committed, as well as to negative character traits such as anger, jealousy and overindulgence.
