Albert Barnes 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)

Cut off - The penalty inflicted on those who transgressed the command may be accounted for on the ground that it was an act of rebellion; but additional light is thrown upon it by the typical meaning assigned to leaven by our Lord (Matthew 16:6).