Festival Prayers-To Serve You In Truth
A miner dug up precious diamonds from the earth, but a treacherous friend substituted worthless stones in their place. When the miner wished to sell them, he found, to his indignation, that he had been betrayed.
Likewise, a man performs good and pious deeds, but he allows evil thoughts to enter his mind. When he takes his place before the Final Judgment, he becomes greatly distressed when shown that his piety is spurious (Chafetz Chaim).