His grandmothers raised their children and expressed affection through the food they lovingly prepared. Nick's grandparents' entire reason for being alive was to create a home for their families, and to give to their children and grandchildren all the opportunities that they had had to forego. The themes of the play are universal. You don't have to be Italian to wonder what we owe the people who love us, or to ask to what degree we, in the modern day, should arrange our lives to be close to our families. For the grandparents in this play, the answers are obvious.
Family is the center, the heart of life.
My siblings are scattered across the globe, from Manhattan to Virginia to Germany. We email each other often, but this is hardly a substitute for weekly family meals. Even Uncle Tony's kids finally moved away. In addition to grappling with existential questions, the play is extremely funny. The audience was cracking up throughout.