This event occurs in Chapter Eighteen, and is when Reuven goes to visit Rabbi Saunders on the first day of Passover. What is of course bitterly ironic about this visit is that recently, Danny, the son of Rabbi Saunders, has announced his intention to not follow in his father's footsteps as his father desired and has decided to study psychology, which his father formerly opposed. There is clearly intense irony in such a situation, as Danny's best friend is becoming a Rabbi whereas Danny himself is not. Note how Rabbi Saunders responds to Reuven's announcement concerning his future career plans:
He looked at me and blinked his eyes. I thought i saw him stiffen for a moment, as though in sudden pain.
Clearly, the way in which Rabbi Saunders is having to confront the loss of his dreams of his son following him and becoming a rabbi is brought into sharp focus when his son's best friend is making the decision that Rabbi Saunders dearly wishes his son himself would make.