The Seven Shepherds–Abraham, Isaac, Jacob, Moses, Aaron, Joseph and David–are seven eminent figures in our history.
Of course, they are also much more than that.
They are personalities who continue to lead the Children of Israel, even in our times, in an invisible fashion.
We invite them to our sukkah because we really feel that they are present among us and are not figments of the past.
Men fall into two categories.
The first is composed of men who act at one point in history.
They belong to the past and their actions have come to a close.
The Seven Shepherds, however, belong to the second category of men: those who have a permanent impact on the Jewish soul, an impact that has lasted up to this very day.
These Shepherds are more than archetypal figures.
A more fitting description is that we, as their descendents, have undergone their influence and have integrated part of their personalities.
–Rabbi Adin Steinsaltz
From “The Three Pilgrim Festivals” p. 271-272, in The Seven Lights by Rabbi Adin Steinsaltz