מדרש אויף דברים 16:15

1)1(Vayikra 23:41) ("And you shall celebrate it at a festival to the L–rd, seven days a year, a statute forever throughout your generations; on the seventh month you shall celebrate it.") "And you shall celebrate it as a festival to the L–rd seven days": Because it is written "And you shall celebrate it as a festival to the L–rd seven days," I might think that one must bring a festive offering (chagigah) all seven days; it is, therefore, written you shall celebrate it" — one day alone.

R. Yossi Haglili says: It is written (Devarim 16:15) "Seven days shall you celebrate ('tachog') to the L–rd your G–d," to include the seven days of Pesach as requiring a chagigah. But perhaps it speaks only of Succoth? (This is not so, for Leviticus 23:41) "And you shall celebrate it as a festival of the L–rd" already speaks of Succoth. How, then, are we to understand "Seven days shall you celebrate"? To include the seven days of Pesach as requiring a chagigah.

One verse (15) states "Seven days shall you eat matzoth," and a second (Devarim 16:8) "Six days shall you eat matzoth." How are these two verses to be reconciled? The seventh day was in the general category (of eating matzoth), and it left that category (in verse 15) to teach about the entire category, viz.: Just as the seventh is optional, so all are optional. But perhaps (the meaning is) Just as the seventh is optional, so the first night is optional? It is, therefore, written (18) "On the first day, on the fourteenth day of the month shall you eat matzoth." Scripture established it as mandatory. It is not the second assumption, then, which is to be accepted, but the first.