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.