Difficulties in Understanding the Mishnah
The Mishnah tells us, "Avrohom came and received the reward of them all." The obvious question is, what reward? The Mishnah says that all the previous nine generations angered Him. The simple explanation cited above does not fully explain this. Avrohom did not receive their reward. He received his award for all the Mitzvos and acts of goodness and kindness he performed.
This may be why at the beginning of the Mishnah, it does not say that "Noach came and received the reward of them all." All of those first nine generations (until Noach) angered Hashem; therefore, there was no reward for him to receive. Why was there a reward from the earlier nine generations waiting for Avrohom?
The Explanation
We first need to understand the difference between the generation of the Flood and the generation of the dispersal.
The generation of the Flood was primarily guilty of interpersonal sins. There was a great deal of robbery and strife between them. Contrast that to the age of dispersal. Their sins, for the most part, were directed against Hashem. The population "stretched out their hands against Hashem, to wage war against Him."
This is the difference between the two groups listed in the Mishnah. Teshuvah, usually translated as repentance, can atone for all sins. However, this only refers to sins between man and G-d. If one hurts or causes damage to his fellow, Teshuvah alone cannot atone until he makes restitution and his fellow forgives him. Even Yom Kippur cannot atone for interpersonal sins. These were the sins of the ten generations from Adam until Noach. They had no atonement. Therefore, they also had no reward for Noach to reap.
The generations from Noach until Avrohom angered G-d. Nevertheless, they deserved a reward since they "behaved with love and friendship with each other." However, because they rebelled against Hashem, they could not receive their reward. Their reward for extending kindness to each other was, as so to speak, stuck. Due to their rebellion, it could not physically reach them ... "until Avrohom came and reaped the reward of all of them."
Avrohom was continually working to reach out to those around him. He dedicated himself to drawing people close to the Shechinah – G-dly Presence. Due to his Divine service, he could rectify and refine the impurity of the nine generations that preceded him. Therefore, he was entitled to all the rewards hanging in abeyance for the preceding nine generations. He was not merely entitled to their reward; it was natural for their reward to manifest itself in Avrohom because of his service.
3. The ten generations from Adam until Noach.
4. The ten generations from Noach until Avrohom. This was the time during which the population was dispersed throughout the world. See Bereishis 11:1-9.
5. See Talmud Sanhedrin 108, a. Also, see Rashi’s comments to Parshas Noach, Bereishis 11:9.
6. See Talmud Sanhedrin 109, a. See also Rashi, ibid.
7. In fact, it means returning (to one’s true self).
8. See Talmud Yoma 85, b. See also the Alter Rebbe’s Shulchan Aruch, Orach Chaim, Chapter 606, Paragraph 1.
9. See Rashi’s comments ibid.
