The passover feast and the subsequent feast of unleavened bread are the greatest feast in the lives of the Israelite for two reasons: It is a remembrance that the Lord passed-over the Israelites when he judged the Egyptians. It is a remembrance that the Lord took them out of Egypt in haste. That month became the first month of the year for the sons of Israel. It should also be understood that a new day began when the sun set on the previous day; therefore, the passover lamb was sacrificed at twilight. The passover lamb was not to be shared with the uncircumcised. For this reason, each lamb was to be consumed by the members of a single household; however, provision was made for two smaller households sharing together in the feast. The calendar was a lunar calendar, which would mean thirteen months to a year and a week would become seven days. So, the festival would begin at twilight as the first full moon of the year was rising, then conclude after a week had passed. The blood on the lintel and two doorposts purified that household in the sight of the Lord. It was believed, by ancient people, that blood warred off evil spirits but blood used in purification was a new way of thinking.
A batch of starter dough was used to leaven the next batch of dough and time was needed for the dough to rise before baking. The new dough was in the mixing bowls when Pharaoh sent the Israelites away; therefore, it was not leavened and had to be baked for food while traveling. Once they settled into the promised land, the Israelites were to eat unleavened bread for seven days, in remembrance, that the Lord took them out of Egypt in haste.
Both the feast of the passover lamb and the feast of unleavened bread would be from this point on a memorial of redemption in the lives of the Israelite. The Lord passed-over the entire congregation on the night of judgment in Egypt and he led the Israelites out of Egypt as an entire congregation; therefore, it was observed with an assembly at the beginning and end of the week to celebrate the Lord’s passover of the sons of Israel and their exodus from Egypt.
When the Egyptians saw that the first born had died in every household in Egypt, they rushed to send away the sons of Israel least they all die. The Egyptians lost great wealth when the Israelites departed. The sons of Israel took with them silver and gold from the land of Egypt. A very large assembly departed Egypt that night and traveled from Rameses to Succoth. This all occurred four hundred years after Jacob and his sons entered the land of Egypt. Thus, the word of the Lord was fulfilled, which he spoke to Jacob, in visions of the night, while he slept at Beersheba, in the land of Canaan, before the sons of Israel took their father and their little ones and their wives to Egypt. (cf.Gn.46:1-7)