Exodus 12:11: "and thus shall you eat it: with your loins girded, your shoes on your feet, an your staff in your hand: and ye shall eat it in haste: It is the Lord's Passover" They didn't have time to wait for the chometz (the leaven or yeast) to rise in their bread, so they quickly mixed flour, salt and spring water, rolled it out and baked it quickly in a very hot oven…about 500 degrees. When it was almost baked, they pierced it with a fork to allow the steam to escape, and it became flattened. This is basicaly the same process Matzah is made by today as the unleavened bread.
Exodus 12:15-50: "Seven days shall ye eateh unleavened bread: even the first day ye shall put away leaven out of your houses: for whosoever eateth leaven from the first day unto the seventh day, that soul shall be cut off from Israel"
Leviticus 23:4-6: "these are the Feasts of the Lord, even holy convocations which ye shall proclaim in their seasons. In the fourteenth day of the first month, at even, is the Lord's Passover. On the fifteenth day of the same month is the Feast of the unleaven bread unto the Lord: seven days ye must eat unleaven bread."
In a study of bible numerics, we find that the number ONE represents "all sufficiency". It was linked to the first Feast of Passover, where we find in that the One God of Israel was All Sufficient to provide the protection that kept the Jews from judgement, and to deliver them from bondage in Egypt. Now we have the second Feast, and the number "2" is related to division and separation. Divide "one" of anything in half, and it separates into 2 parts. God created light, and it separated the darkness; then He created 2 lights to divide one for the day, and one for the nights…the sun and the moon. This implies that the 2nd Feast, the Feast of the unleavened bread, is related to separation; the separation of clean from unclean; holy from unholy; the old from the new.
From a National viewpoint, it was an agricultural observance, a time when all the old grain in the barns, the mills and from the house was thrown away to avoid being mixed with the new grain of the future harvest. Originally, Passover and Feast of unleavened bread were two separate Feasts, but because one began immediately after sunset, (which was the beginning of a new day on the Jewish calendar), the 2 Feasts became acknowledged and celebrated as one. The Passover lamb was slain around 3pm toward the close of Nisan 14, and by the time it was cooked and ready to serve, it was past sunset and already the beginning of Nisan 15, the Feast of unleavened bread.
Biblically speaking, leaven is almost always portrayed as a type of sin.
Prophetically, this Feast pointed to a time God's people would separate and cleanse themselves from the heathen and from their sinful idol worship. It pointed to a time that God would demand holiness from His people…"be ye holy for I am holy". God always wanted His people separated from the heathen. In the new covenant, Rabbi Saul exhorted the Jews in I Corinthians 5:7; "purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ, our Passover is sacrificed for us. Therefore, let us keep the Feast, not with old leaven…" he's talking about carnality and sin…"Neither with leaven of malice and wickedness; but with the unleavened bread of sincerity and truth."
In its Spiritual application, this Feast speaks to us about spiritual sanctification and separation from the world and carnality. We, who believe and have already applied the blood of our Passover, Yeshua, to the door of our hearts and lives, need to move on to the second Feast of separation by stepping into the waters of baptism, where our sins can be remitted, (Acts 2:38), washed away; separated from us; guilt and shame cleansed from our lives; a new creature in Christ, separated from the bondage of and stain of sin…and we can keep the Feast without leaven.