Lev. 23:5-6
"In the fourteenth day of the first month at even is the Lord's passover. And on the fifteenth day of the same month is the feast of unleavened bread unto the Eternal: seven days ye must eat unleavened bread."

(When God called His nation out of slavery under Moses it was for the purpose of "sacrificing the Passover.") Ex. 3:18, 5:1-3, Ex 12

(The Passover and the Exodus- are pictures of Christ
Egypt is a type of sin; Pharoah is a type of Satan the Devil; Moses appears in two shadowy roles (1) as a type of God the Father, and (2) as a type of Jesus Christ, as the shepherd of God's people.
Moses and Aaron are also seen as shadowy types of the future 'two witnesses' of Rev 11. The sacrificial lamb is a type of Jesus Christ (Isa 53:7). The shed blood of the lamb on the lintels and door posts of the Israelites' houses is a symbol of Christ's shed blood atoning for our sins, to pass over those who ask Christ for forgiveness.
The death angel symbolizes God's judgments against unrepentant sinners who will not obey God (Ezek 9:2-11, Rev 14: 17-20).

(Once God had broken the hold of Pharoah over the Israelites, they were THRUST out of Goshen.)

(Leaven is also a type of sin.)

Matt 16:5-12
Jesus said, "Take heed and beware of the leaven of the Pharisees and of the Sadducees."

(Unleavened bread pictures sinlessness; humility, and absence of vanity, pride and sin.)

John 6:48-51
"I am that bread of life. Your fathers did eat manna in the wilderness, and are dead.
This [pointing to himself] is the bread which cometh down from heaven, that a man may eat thereof and not die.
I am the living bread which came down from heaven; if any man eat of this bread, he shall live for ever; and the bread that I will give is my flesh, which I will give for the life of the world."

(The church during the second and third centuries rejected God's Sabbaths (including the annual holy days) and adopted the pagan festivals of the Gentiles. The church then began to observe Easter inplace of the Passover, and other pagan holidays as well.There began great persecution during the days of Constantine, who himself had been a sun worshipper,and the true church was forced to go underground. a decree had been issued that Christians were not to be found Judaizing by observing the Jewish ways.