Pirkei Avot, Ethics of the Fathers, is a tractate of the Mishnah that comprises advice from the sages on ethical, political, and spiritual matters. Hillel's dictum encapsulating the conflict between self-interest and helping others, "If I am not for myself, who will be for me? But if I am only for myself, what am I? And if not now, when?" (1:14), is one of its most celebrated sayings.
Since gaonic times (late 6th – 11th centuries), Jews have had the custom to study one chapter of Pirkei Avot every Shabbat between Pesach and Shavuot. More recently the practice has been extended through the whole summer to Rosh Hashanah.
The tractate's six-chapter structure lends itself perfectly to the six Shabbatot between Pesach and Shavuot. The idea behind this custom is to refine one's character before re-enacting the giving of the Torah on Shavuot. Reading and discussing a chapter of Pirkei Avot on long Shabbat afternoons raises ever-relevant moral issues and is a powerful lens through which to view the events of the previous week.