The Feast of Unleavened Bread is a week long celebration which begins with the firstborn travelling to the Sanctuary in Jerusalem and removal of all yeast bread products from the home and property. The yeast bread is then replaced with unleavened bread. This celebration is now celebrated as communion taken in remembrance of the sacrifice of Jesus.

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. (Exo 23:14,17, 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