From the book Advice:
Rabbi Nachman: ADVICE (LIKUTEY ETZOT) by Rabbi Nathan of Breslov

Eating

3) When a person attains perfect mastery of the Holy Tongue and guards the Holy Covenant in purity he has the power to stir up the sparks of the letters which exist throughout the Creation. All the pleasure he has from eating and drinking and other enjoyments comes only from the sparks of the letters. His heart is illumined and his face becomes so radiant that people are moved to return to God simply by seeing it. Everyone who looks at his face sees his own reflected there as if in a mirror —and sees, in contrast, how far sunk in darkness he is. Without a single word of preaching he will want to be released from his darkness —all through seeing this person’s face (19: 7-9).