Pesachim 38 - Should you own your matzah?
When one separates "challah," the kohen’s portion of the dough, it has to be his dough, because the Torah said, "When you will eat your bread." Rav Assi said that the same is true for matzah at the Seder - one has to own it. Rav Pappa objected: "Does it ever say, ‘your own’ about matzah?" Rava told him that actually it does. The same word, "bread" is used to describe matzah, "bread of affliction" and challah, the priests portion, which makes their laws the same. This has a practical ramification: one cannot fulfill the mitzvah of eating matzah at the Seder with stolen matzah.
The offering of the Nazirite included unleavened bread. Can one use this bread for his Seder? The answer is that if he prepared it for himself, then he cannot eat it at the Seder, but if he prepared it to sell to others, then he can use it himself. This seems paradoxical. However, it is logical.
The Torah said, "Watch your matzah," that is, guard it for the sake of the Seder. If he prepared the matzah for himself, he watched it for a Nazirite, not for the Seder - thus, he cannot eat it. But if he prepared it for others, he had a thought in the back of his mind, that if he cannot find buyers, he will use it for the Seder. Therefore, he watched with the intention of possibly using it for Seder, and now he can indeed eat it.
Art: An earthenware tankard, a bread roll, a pewter dish of hazlet by (after) Jacob Fopsen Van Es