In a Nutshell
The Feast of Passover and Unleavened Bread commemorates God's deliverance of Israel out of Egypt. Pesach (PAY-sahk) means to literally "pass over." The Passover meal, seder (SAY-der), commemorates the Israelites' deliverance from slavery in Egypt. The LORD sent Moses to lead the children of Israel from Egypt to the Promised Land. When first confronted by Moses, Pharaoh refused to let the people go. After sending nine plagues, the LORD said the firstborn males of every house would die unless the doorframe of that house was covered with the blood of a perfect lamb. That night, the LORD "passed over" the homes with blood on the doorframes. The tenth plague brought death to the firstborn sons of Egypt, even taking the life of Pharaoh's own son. Finally, Pharaoh let the children of Israel go. Passover was to be a lasting ordinance for generations to come. In Leviticus, the LORD said that on the fourteenth day of the first month (of the religious new year) the LORD's Passover was to begin at twilight.
In Leviticus 23, Hag HaMatzot (Hawg-MAHT-zot) or Hag HaMatzah, also known as the "Feast of Unleavened Bread," is mentioned as a separate feast on the fifteenth day of the same month as Passover. Today, however, the feasts of Pesach, Unleavened Bread, and Firstfruits have all been incorporated into the celebration of Passover, and reference to Passover means all three feasts. Passover is celebrated for eight days, Nisan 14-21. The LORD said that for seven days the children of Israel must eat unleavened bread. This bread, made in a hurry without yeast, represents how the LORD brought the Israelites out of Egypt in haste. In Scripture, leaven also represents sin. Orthodox Jews believe that not only is eating bread with leaven unlawful during the Feast of Unleavened Bread, but even having leaven present in one's house or apartment is forbidden. Today, cleansing the house before Passover is often a symbolic search to remove any hypocrisy or wickedness. Unleavened Bread is one of the three pilgrimage feasts when all Jewish males were required to go to Jerusalem to "appear before the LORD." (Deut. 16:16)
On Yom HaBikkurim (Yome Hah-Bee-koo-REEM) people offered the first ripe sheaf (firstfruits) of barley to the LORD as an act of dedicating the harvest to Him. On Passover, a marked sheaf of grain was bundled and left standing in the field. On the next day, the first day of Unleavened Bread, the sheaf was cut and prepared for the offering on the third day. On this third day, Yom HaBikkurim, the priest waved the sheaf before the LORD. Counting the days (omer) then begins and continues until the day after the seventh Sabbath, the 50th day, which is called Shavuot or Pentecost (the next feast on the calendar). Jewish people rarely celebrate Yom HaBikkurim today, but it has great significance for followers of Jesus as the most important day of the year, the day of Jesus' resurrection.