John Calvin Commentary Exodus 12:15

"Seven days shall ye eat unleavened bread; even the first day ye shall put away leaven out of your houses: for whosoever eateth leavened bread from the first day until the seventh day, that soul shall be cut off from Israel." — Exodus 12:15 (ASV)

Whoever eats leavened bread. This law specifically refers to the keeping of the Passover. God had previously forbidden the use of leaven, and He now enacts the punishment to be inflicted if anyone neglects the prohibition and mixes leaven with the Passover feast.

But it is not without reason that we have postponed to this section what Moses joined with the institution of the Passover, for our proposed plan demands that the political laws, which enforce God’s worship by prescribing punishments, should occupy their own distinct place.

From the punishment, it appears that although it may in itself be a trivial matter to abstain from leaven (as Paul teaches that bodily exercise profiteth little, 1 Timothy 4:8), yet, since in this ceremony the redemption of the people was commemorated, it was a very serious crime not to observe whatever God had prescribed. We must assess the importance of the rites of the law by their purpose.⁶⁹

⁶⁹ “Selon leur fin, et leur verite.” — .” — Fr..