Why did Israel eat unleavened bread after Passover?
Israel ate unleavened bread for seven days after Passover to picture a nation whose sins had been atoned for and cleansed. The unleavened bread portrayed them as unleavened—forgiven and, so far as God was concerned, without sin. It was a visual lesson tied to the Passover in Egypt.
Les explains that the practice went all the way back to the Passover in Egypt, and the very next day after Passover was the seven days of unleavened bread. The people were now to be pictured as a nation whose sins had been atoned for or cleansed, and they were to picture that with the unleavened bread. Les then brings Paul's analogy into our teaching today: we have to look at sin in our individual lives and in the life of the church, just like the leaven in the bread of Egypt. Paul's words say, “That you may be a new lump as you are unleavened.” To be unleavened means we have been forgiven, we have been cleansed, and we are, so far as God is concerned, without sin. But if we leave a little bit of leaven in our life, it isn't too long until it begins to expand and expand and consume us again. So even as Christ our Passover is sacrificed for us. Les also points to what happened on the doorposts, on the two side posts and one on the top; in your mind's eye you can picture the outline of the cross, and he is sure that is what God had on His mind.
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.