This is the period of the "the Counting of the Omer," a time for introspection and refinement of one's character in preparation for the giving of the Torah. The study and application of the moral teachings of Avot serves as a preparation for receiving the Torah on Shavuot. For "the Torah will only dwell in one free of negative traits and filled with virtues"
Midrash Shmuel; The Rebbe in Biurim
It is customary to recite the following, before studying the chapter:
All of Israel have a share in the World to Come, as it says (Isaiah 60:21), your people are all righteous; they will inherit the Land forever; they are the branch of My planting, the work of My hands in which I take pride. (Sahedrin 11:1)
All of Israel:
The following are a few of the reasons given for the custom to read "All of Israel" before studying Avot:
• One might have thought that Avot, which demands that one go beyond the letter of the law, is not applicable to every person. We therefore begin our study of Avot with a Mishnah that praises all of Israel, implying that every Jew can and must fulfill the words of Avot (The Rebbe in Biurim).
• It is because of his loftiness - as expressed in the passage All of Israel - that each Jew is capable of implementing the challenging teachings of Avot (Maharal; The Rebbe in Biurim)
• Avot is read as a preparation to receive the Torah on the holiday of Shavuot. The first step in this preparation must be to engage in acts of love towards one's fellow. We therefore read All of Israel, which helps us appreciate the value and loftiness of our fellows and overcome our natural biases (The Rebbe in Biurim).
The World to Come:
"The World to Come" refers to the Messianic Era, when every soul that has ever lived will return to the physical world and be clothed in a body, enjoying the fulfillment of G-d's ultimate plan: the creation of a Divine dwelling in the physical world (see Bartenura, Midrash Shmuel).
Even one who has committed capital crimes is admitted into the World to Come after receiving his punishment (Rambam).
Are all righteous, Regardless of their fulfillment of mitzvot or lack thereof (Maharal).
Will inherit the land of eternal life (Maharal).
Will inherit the land forever. An inheritance does not require any action on the part of the inheritor. Similarly, all of Israel, by virtue of their very being, are inheritors of the land forever, i.e., the World to Come and eternal life.
The Branch of my planting.
Just as a planting must be tended to in order to grow properly, the individual - despite his inherent share in the World to Come - must put forth his own effort in order to actualize his full potential (The Rebbe in Biurim). Although every person has a share in the World to Come, the quality of that share is dependent upon one's actions (Bartenura).
Holtzberg Memorial Edition