The Feast of Unleavened Bread is a week long celebration which begins immediately after Passover, with the firstborn travelling to the Sanctuary in Jerusalem and removing all yeast bread products from the home and property. The yeast bread is then replaced with unleavened bread. This celebration is now commonly celebrated as communion taken in remembrance of the sacrifice of Jesus. The Jewish calendar changes yearly so there is no definite date to start each year like many American holidays.  “Passover, the Feast of Unleavened Bread, and the Day of First Fruits.
These three festivals speak of three stages of salvation: justification, sanctification and glorification.
    Yeshua has already fulfilled all three. Now it's our turn!
As Romans 6:5 says, "If we have been united with [Messiah] like this in his death,
we will certainly also be united with him in his resurrection."
Let's pray.
Turn to Leviticus 23.
Pesach begins on the 14th of Nisan, the first month, as it is written:
    5 The LORD's Passover begins at twilight on the fourteenth day of the first month.
It is immediately followed by Chag HaMatzot, the Feast of Unleavened Bread:
    6 On the fifteenth day of that month the LORD's Feast of Unleavened Bread begins;
    for seven days you must eat bread made without yeast”.
(Pesach, Chag HaMatzot, Yom HaRaysheet: Dead to Sin, Alive to Him
Shabbat, April 22, 2000, https://www.lehigh.edu/~gdb0/simcha/firstf00.htm#:~:text=5%20The%20LORD's%20Passover%20begins,eat%20bread%20made%20without%20yeast).

The Feast of Unleavened Bread is one of the first three compulsory pilgrimage feasts, traditionally a week long observance which involves men travelling to the Sanctuary in Jerusalem to present themselves before the Lord.  The Lord specifies three feasts to be kept for Him in each year which are

1. Passover
2. The Feast of Unleavened Bread
3. The Feast of the Harvest.

All males are to be present at the feasts.

• Exodus 23:14 Three times thou shalt keep a feast unto me in the year.
• Exodus 23:15 Thou shalt keep the feast of unleavened bread: (thou shalt eat unleavened bread seven days, as I commanded thee, in the time appointed of the month Abib; for in it thou camest out from Egypt: and none shall appear before me empty:)
• Exodus 23:16 And the feast of harvest, the firstfruits of thy labours, which thou hast sown in the field: and the feast of ingathering, which is in the end of the year, when thou hast gathered in thy labours out of the field.
• Exodus 23:17 Three items in the year all thy males shall appear before the LORD God.
• Exodus 23:18 Thou shalt not offer the blood of my sacrifice with leavened bread; neither shall the fat of my sacrifice remain until the morning.
• ​Exodus 23:19 The first of the firstfruits of thy land thou shalt bring into the house of the LORD thy God. Thou shalt not seethe a kid in his mother's milk.

(Exo 34:22, Deut 16:16). This is considered a convocation observance and is considered as a Sabbath day which means there is no work to be done during this Holy time.The first day is the 15th day of the first month (Abib/Nisan) of the Feast of Unleavened Bread. Lev 23:7, Num 28:17-18. This feast signifies the importance of the firstborn's dedication to the Lord's service as a celebration of release from bondage in Egypt (Exo. 13:6-10).
All bread with leaven (hametz) is removed. Leaven is yeast or baking powder-anything that bakes bread rise during the baking process. The bread is then replaced with unleavened bread (matzah)with no leaven in it. The day that this observance begins is traditionally the seventh day Sabbath (the day after the crucifixion of Jesus Christ) which makes it a high Sabbath day (John 19:31). Jesus spent the day in the tomb resting on this Sabbath. Today the Feast of Unleavened Bread is considered a rememberance to honor the sacrifice made representative of the sinless nature of Jesus related to us being released from the bondage of sin as Jesus is the bread of life (John 6:32, 48-51). The leaven bread (hametz) is said to represent the sin in your life replaced by Jesus is the sinless bread of life (unleavened bread/matzah) which overcame by becoming a sacrifice for sin and thereby removing corruption of sin in your life and replacing it with Jesus (I Cor. 5:8). Many churches celebrate the Passover meal by offering Communion as the Lord's Supper thereby remembering the sacrifice that Jesus made for you at the cross (Luke 22:19) as their message during this ceremony. This Feast of Unleavened bread was during the time of the latter rain (March/April) which was the day that Israel started eating from the old corn and the daily manna the Lord provided during their escape from Egypt ended.
(Josh 5:11) (Biblical Feasts, 2016).

Reference: The Biblical Feast Days. Retrieved on Feb. 29, 2016. http://biblelight.net/feasts.html