I welcome to my table the saintly guests, Abraham, Isaac, Jacob, Moses, Aaron, Joseph, and David (Machzor of Succos).
Why is Succos unique among all the festivals in that we invite the Patriarchs to share the celebration with us?
Succos is the festival of the harvest. All the efforts that had been invested in the land - plowing, watering, fertilizing, weeding, pruning, and finally harvesting - have culminated in an abundant harvest, and we are now ready to enjoy the fruits of our labor.
God wants us to enjoy worldly goods, but to do so in a manner that befits a spiritual people, a kingdom of priests and a holy nation. While there are many laws that pertain to working the land and tithing its produce, these do not yet assure our spirituality. Much of the Torah does not relate to specific law, but consists of a narration of the lives of Seven great leaders, whom we invite into our succah, as it were, because they are the role models whom we are to emulate. They were all people of means, yet their lives were dedicated to sanctity, and their worldly possessions did not distract them from their primary spiritual goals.
Each of them excelled in a particular attribute, although they all shared in each other's attributes. For example, Abraham's, benevolence, included majesty of benevolence, and David's majesty, included benevolence of majesty; yet they and all the intermediate leaders were paragons of humility and self-effacement. We invite the great leaders to our succah to remind us to fashion our lives after theirs.