The plague that is mentioned here was the tenth and final plague that God sent upon the land of Egypt that hard hearted Pharaoh might relent and release the nation of Israel from his grip so that they might be set free to serve God in the wilderness (Ex. 7:16).

Ex. 12:29: At midnight the Lord struck down all the firstborn in Egypt, from the firstborn of Pharaoh, who sat on the throne, to the firstborn of the prisoner, who was in the dungeon, and the firstborn of all the livestock as well.

The significance of this feast was of enormous importance, a FORESHADOWING of the unblemished, spotless LAMB that was to come, the sacrifice for the sins of mankind. John the Baptist attested to this:

John 1:29: The next day John saw Jesus coming toward him and said, "look, the Lamb of God, who takes away the sin of the world!"

The blood of the male lamb that was to be applied on the doorposts and lentils signified that precious and holy blood of Christ that was yet to be shed for His people, the nation of Israel and for all men.

Heb. 9:12: He did not enter by means of the blood of goats and calves; but He entered the Most Holy Place once for all by His own blood, thus obtaining ETERNAL REDEMPTION.
13: The blood of goats and bulls and the ashes of a heifer sprinkled on those who are ceremonially unclean sanctify them so that they are outwardly clean.
14: How much more, then, will the blood of Christ, who through the eternal Spirit offered Himself unblemished to God, cleanse our consciences from acts that lead to death, so that we may serve the living God!

The bitter herbs included in the meal signified the slavery and suffering that was the portion of the Israelites and foreshadowed slavery to SIN, that from which Christ died to set us free. Jesus Himself taught the Jews that had believed in Him this:

John 8:34-36: Jesus answered them, "Most assuredly, I say to you, whoever commits sin is a slave of sin. And a slave does not abide in the house forever, but a son abides forever. Therefore if the Son makes you free, you shall be free indeed.

Paul expounds on what the 'leaven' signified in his epistle to the Corinthians:

1 Cor. 5:5-8: "It is actually reported that there is sexual immorality among you, and such sexual immorality as is not even named among the Gentiles - that a man has his father's wife!
2: And you are puffed up, and have not rather mourned, that he who has done this deed might be taken away from among you.
3: For I indeed, as absent in body but present in spirit, have already judged (as though I were present) him who has so done this deed.
4: In the name of our Lord Jesus Christ, when you are gathered together, along with my spirit, with the power of our Lord Jesus Christ,
5: deliver such a one to Satan for the destruction of the flesh, that his spirit may be saved in the day of the Lord Jesus.
6: Your glorying is not good. Do you not know that A LITTLE LEAVEN LEAVENS THE WHOLE LUMP?
7: Therefore purge out the old leaven, that you may be a new lump, since you truly are unleavened. For indeed Christ, our Passover, was sacrificed for us.
8: Therefore let us keep the feast, not with old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth.

Paul, in writing to the Corinthian church that not only did not shun and remove the sexually immoral believer, but also glorified the sin, had strong words to deliver with regard to the sinning believer. He was to be DELIVERED TO SATAN for the destruction of his flesh SO THAT his SPIRIT MIGHT BE SAVED. This was the way they were to observe the Passover - by purging out the old leaven of malice, sin, wickedness and ungodliness. He reiterates this...

1 Cor. 5:11: But now I have written to you not to keep company with anyone named a brother, who is sexually immoral, or covetous, or an idolater, or a reviler, or a drunkard, or an extortioner - NOT EVEN TO EAT WITH SUCH A PERSON.
12: For what have I to do with judging those also who are outside? Do you not judge those who are inside?
13: But those who are outside God judges. Therefore "put away from yourselves the evil person."

The purging of the old leaven involved judgment by the Church so that sin might be expunged from their midst.

SINCERITY and TRUTH were to be embraced instead.

The Church would do well to adhere to this commandment. Judgment by the Church of the Church is Scriptural!

1 Cor. 6:1: Dare any of you, having a matter against another, go to law before the unrighteous, and not before the saints?
2: Do you not know that the saints will judge the world? And if the world will be judged by you, are you unworthy to judge the smallest matters?
3: Do you not know that we shall judge angels? How much ore, things that pertain to this life?

In his letter to the Colossian church, Paul outlined what they were NOT allowed to be judged on.

Col. 2:16: Therefore do not let anyone judge you by what you eat or drink, or with regard to a RELIGIOUS FESTIVAL, a New Moon celebration or a Sabbath day.
17: These are a SHADOW of the things that were to com; the REALITY, however, is found in CHRIST.

Christ FULFILLED the shadows of the Law and its sacred ordinances at the cross, being the reality and substance and the culmination of its ordained feasts and festivals, the Lamb sacrificed for our sin. The Law, the OLD covenant, has PASSED AWAY and been replaced by the new and better covenant mediated by the BLOOD OF CHRIST;

Heb. 9:13: For if the blood of bulls and goats and the ashes of a heifer, sprinkling the unclean, sanctifies for the purifying of the flesh,
14: how much more shall the blood of Christ, who through the eternal Spirit offered Himself without spot to God, cleanse your conscience from dead works to serve the living God?
15: And for this reason He is the Mediator of the new covenant, by means of death, for the redemption of the transgressions under the first covenant, that those who are called may receive the promise of the eternal inheritance.

Heb. 10:1: The Law is only a shadow of the good things that are coming - not the realities themselves. For this reason it can never, by the same sacrifices repeated endlessly year after year, make perfect those who draw near to worship.

Gal. 4:9: But now that you know God - or rather are known by God - how is it that you are turning back to those weak and miserable forces? Do you wish to be enslaved by them all over again?
10: You are observing SPECIAL DAYS and months and seasons and years!
11: I fear for you, that somehow I have wasted my efforts on you.

Christ mediated the NEW covenant sealed by His own precious blood. It is therefore a redundant practice to enact the Passover mean under the New Covenant. And much more so when the Church is immersed in malice and all manner of wickedness and uses this ritual initiated for the nation of Israel as a CLOAK to cover its own ungodliness, much in the same way as whitewashed tombs are full of filth and dead men's bones. (Matt. 23:27)

The Church does not need to introduce gimmicks and 'tourist attractions' to lure in new congregants or have tangible elements to validate its existence. The only physical elements the Church as been commanded to partake of are the symbols of the body and blood of Christ.

INSTEAD:

Col. 3:8: But now you yourselves are to put off all these: anger, wrath, malice, blasphemy, filthy language out of your mouth.
9: Do not lie to one another, since you have put off the old man with his deeds,
10: and have put on the new man who is renewed in knowledge according to the image of Him who created him.

The leaven of malice and sin is to be substituted with the unleavened bread of righteousness, sincerity and truth, the old substituted by the new.

THIS is the will of GOD.