Why should Christians celebrate the Passover?

Jesus Christ and the apostles kept the Passover. What does Passover mean for Christians today?

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The first of God's seven annual festivals is the Passover (Leviticus 23:5In the fourteenth day of the first month at even is the LORD's passover.
See All...). Passover falls in early spring in the Holy Land and is a reminder of how God spared His people from death in Egypt. To rescue His people from slavery, God took the lives of all the firstborn Egyptian males (Exodus 12:7And they shall take of the blood, and strike it on the two side posts and on the upper door post of the houses, wherein they shall eat it.
See All..., 26-29) but passed over the Israelites' homes that had the blood of a sacrificed lamb on their door frames.

The blood of the Passover lamb foreshadowed the sacrifice of Jesus Christ, which passes over the sins of people who repent in order to spare them from eternal death. The New Testament makes clear that Christ is the true Passover Lamb (compare Exodus 12:21Then Moses called for all the elders of Israel, and said unto them, Draw out and take you a lamb according to your families, and kill the passover.
See All... with 1 Corinthians 5:7Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us:
See All...). In observing His last Passover with His disciples, Jesus explained that the symbols of bread and wine represent His body and blood, offered by Him for the forgiveness (or passing over) of our sins and the death penalty our sins have earned for us (Matthew 26:26-28 [26] And as they were eating, Jesus took bread, and blessed it, and brake it, and gave it to the disciples, and said, Take, eat; this is my body.
[27] And he took the cup, and gave thanks, and gave it to them, saying, Drink ye all of it;
[28] For this is my blood of the new testament, which is shed for many for the remission of sins.

See All...; Mark 14:22-24 [22] And as they did eat, Jesus took bread, and blessed, and brake it, and gave to them, and said, Take, eat: this is my body.
[23] And he took the cup, and when he had given thanks, he gave it to them: and they all drank of it.
[24] And he said unto them, This is my blood of the new testament, which is shed for many.

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The death of Christ actually took place during the daylight hours that followed the Passover evening—which was still the same date according to Hebrew sunset-to-sunset reckoning. Christ was sacrificed on Passover.

The New Testament Passover is a memorial of the suffering and death of Jesus Christ. This is also when baptized members of the United Church of God renew our agreement to come under the blood of Jesus Christ, the perfect Passover Lamb, for the forgiveness of our sins. We approach this period of the year with deep spiritual introspection. We commemorate the Passover on the 14th day of the first month of the sacred year with a service based on the instructions of 1 Corinthians 11:23-28 [23] For I have received of the Lord that which also I delivered unto you, That the Lord Jesus the same night in which he was betrayed took bread:
[24] And when he had given thanks, he brake it, and said, Take, eat: this is my body, which is broken for you: this do in remembrance of me.
[25] After the same manner also he took the cup, when he had supped, saying, This cup is the new testament in my blood: this do ye, as oft as ye drink it, in remembrance of me.
[26] For as often as ye eat this bread, and drink this cup, ye do shew the Lord's death till he come.
[27] Wherefore whosoever shall eat this bread, and drink this cup of the Lord, unworthily, shall be guilty of the body and blood of the Lord.
[28] But let a man examine himself, and so let him eat of that bread, and drink of that cup.

See All... and the Gospel accounts of the New Testament Passover that Christ instituted.

This solemn service begins with a brief explanation of its purpose, followed by foot-washing (based on Christ's example and instructions in John 13). Then the minister gives an explanation of the symbols of the Passover, unleavened bread and wine, which represent the body and blood of our Savior. Each baptized member of the Church eats a small piece of the unleavened bread and drinks a small glass of the wine (Mark 14:22-24 [22] And as they did eat, Jesus took bread, and blessed, and brake it, and gave to them, and said, Take, eat: this is my body.
[23] And he took the cup, and when he had given thanks, he gave it to them: and they all drank of it.
[24] And he said unto them, This is my blood of the new testament, which is shed for many.

See All...).

Christians who observe this annual memorial marking Jesus' death (1 Corinthians 11:26For as often as ye eat this bread, and drink this cup, ye do shew the Lord's death till he come.
See All...) are reminded that eternal life is possible only through Him (John 6:47-54 [47] Verily, verily, I say unto you, He that believeth on me hath everlasting life.
[48] I am that bread of life.
[49] Your fathers did eat manna in the wilderness, and are dead.
[50] This is the bread which cometh down from heaven, that a man may eat thereof, and not die.
[51] 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.
[52] The Jews therefore strove among themselves, saying, How can this man give us his flesh to eat?
[53] Then Jesus said unto them, Verily, verily, I say unto you, Except ye eat the flesh of the Son of man, and drink his blood, ye have no life in you.
[54] Whoso eateth my flesh, and drinketh my blood, hath eternal life; and I will raise him up at the last day.

See All...; Acts 4:10-12 [10] Be it known unto you all, and to all the people of Israel, that by the name of Jesus Christ of Nazareth, whom ye crucified, whom God raised from the dead, even by him doth this man stand here before you whole.
[11] This is the stone which was set at nought of you builders, which is become the head of the corner.
[12] Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved.

See All...). Jesus' sacrifice is the starting point for salvation and the foundation of the annual feast days that follow. The next one is the Feast of Unleavened Bread.