Every year, in honor of Passover, members of the Baal Shem Tov’s household purchased a large quantity of new cups to be used for the duration of the holiday.

Of course, following Jewish law, the glasses that were to be used would first be immersed in a mikvah.

The glasses came in a variety of shapes and sizes. Now, in Jewish literature there is a system for measuring liquids, with specific names for the various amounts. In the Baal Shem Tov’s home, the glasses were referred to by the Jewish name for the amount of liquid they were able to contain. Thus, a glass that contained three ounces or so was called a revi’it glass, etc.

Before Passover, the Baal Shem Tov would look through the glasses and instruct which cups could be set upon the table and which should be set aside. He provided no reasons for his directives, but everyone knew that surely his reasoning was sound.

Thus passed the first seven days of Passover.

Now, the final meal on Passover, known as Moshiach’s meal, was special. It was open to the public; everyone who passed through the sage’s door was free to enter and partake of the festivities. Before the meal began, the Baal Shem Tov instructed that a certain cup be removed from the table because it had not been immersed.

During the meal, a newcomer entered and asked for some wine. “Sorry,” he was told, “but there are no more clean cups.”

“What do you mean?” he asked with surprise, pointing to the cup that had been set aside, “I see a clean cup right over here that no one is using!”

“Oh,” he was told, “that cup has not been immersed in the mikvah and must not be used.”

“It doesn’t matter,” he replied dismissively, reaching for the cup.

At that point, the Baal Shem Tov, who had hitherto been silent during the exchange, spoke with sadness. “He just testified about himself.”

The words were mysterious to everyone aside from the man himself. Hearing the rebbe’s gentle words of rebuke, he admitted his shortcoming. It was true. He and his wife were not particular about the laws of family purity, which require a previously menstruant woman to immerse in a mikvah before being intimate with her husband.

Inspired, they resolved to mend their ways.

Translated from Sefer Hasichot, 5702.