Step 1: Context.
In the story "The Bet," the lawyer spends fifteen years in voluntary imprisonment to win a bet against the banker.
Step 2: Explanation.
When the banker read the lawyer's final note, he understood that the lawyer had gained spiritual knowledge and lost interest in money. The banker felt ashamed of his greed and material desires.
Step 3: Conclusion.
Thus, the banker wept out of guilt and realization of the lawyer's wisdom.