Easter is such a big deal for Christians because it is the heart of the story. It is what Christianity is all about.
Whilst Christmas is a lovely celebration; we recognise Jesus came to Earth, the son of God, fully man, fully God etc etc. the reason why Christians are Christians and call themselves Christians is because Christ died for their sins.
History proves that Jesus existed. A man, called Jesus was alive at the time the bible claims that He was, and He caused quite a stir. That much can be proven.
What makes this Jesus man particularly significant is the fact that He claimed He was the son of God. If you think carefully about it; the place and culture in which He was saying this, the gravity of the statement He was making and the fact that saying such a thing would have a MASSIVE impact on the people who belonged to the culture He was speaking to... you have to think about it...He was either completely nuts - as in the guy wanted the people of Nazareth and Bethlehem and Judea to kill Him, or He was telling the truth.
If He was telling the truth; which is what Christians believe, if He was telling the truth, then this is what He was saying:
Jesus was claiming that the root of all problems faced in the world, in this life, all of them, could be found in sin, something which is found within us.
Jesus was saying that it was sin that caused pain, distrust, corruption, dishonesty, poverty, harm, and general disaster.
So if Jesus was telling the truth about Himself and about sin, then, as He said, the only permanent solution to the problem would be Himself.
Hear me out. In humbling Himself; that is in coming in the form of a man, with all the temptations, exposure to sin and its effects and ordinary people, and then dying as He did, he provided us with the grace to live SIN-FREE, dealing with the source of the world's problems permanently, so that sin could no longer cause any problems.
Now, don't get me wrong. I am fully aware, that some Christians, in fact, A LOT of Christians (myself included), have acted sinfully (outside of God's will) and as a result done A LOT of stupid things. But here's the difference between how Christians deal with sin, and how non-Christians deal with sin.
In my experience, when non-Christians sin, or, as a lot would say 'do bad things' or 'do the wrong thing', they will say this; 'I couldn't help it', or 'it's human nature'. There is an acknowledgement that what happened was wrong, and more often than not they will also say something along the lines of 'I won't be doing it again though', or 'I'll try harder next time not to'.
When Christians sin, they also acknowledge that they did the wrong thing, but they acknowledge that the wrong thing was not only done against the person or persons or object, but against God, because they were falling short of His standard, i.e. sinning. This is significant because when we acknowledge that we did the wrong thing before God, we are also acknowledging that there is a penalty we are required to pay for our sin. God being Good (without sin) and just (fair - as in, He can only accept Good), means that when we sin, He has to acknowledge it. He can't just gloss over it, because immediately He's not always Good, because He's allowing sin. It's like a judge saying to a murderer, 'no you're good, be on your way', it immediately makes us question how Good God is. And when God acknowledges our sin, He acknowledges that there is a penalty we have to pay for it.
BUT, because God is merciful and gracious, He didn't want us all to pay the full wages of our sin (death - eternal death, eternal separation from Him). So He looked for a way for us - if we wanted to - to be reconciled to Him, without compromising on His Goodness and Fairness. So what He did, is that He put Himself in our place. He gave us His son, the human embodiment of Himself on this Earth (Jesus), to go through the same everyday struggles as us; betrayal, hunger, friendship, family, even the paying of taxes, and yet NOT sin, so that all the sins we have ever and will ever commit, would be accredited to Him - as in, we did the crime but He did the time - so that we could still have a relationship with Him.
Got it yet?
He gave up a part of Himself, so that we could be part of His family.
So when Christians acknowledge their sin before God, they acknowledge the penalty that they owe, but even greater than that, they acknowledge that the penalty they owe (to God), has already been paid, so they can still be in relationship with God despite their sin, and so that next time, when the opportunity to commit that same sin arrives (and it always does, trust me), they can be sure, that the person who went before them, Jesus; God Himself, already went through temptation and resisted it, so that there is another way to do things, and they don't have to give into human nature; therefore meaning, that those impulses they have always given into, are not the only way to live, that they don't have to be in a sin-guilt-sin-guilt cycle, but that they can have a new future shaped by a new way of doing things, with the help of someone BETTER than themselves: Jesus.
To sum up why Christians celebrate Easter. Easter is a celebration, a party if you will, at which Christians remember and get excited about the fact that God loved them so much, that despite all their idiocy; the silly day-to-day sins they commit and mistakes that they make, He gave Himself up for them so that they could be free from a sin-FULL lifestyle, and live one of grace, with forgiveness in abundance, available every nanosecond.
Happy Easter - Jesus died to set you free, He said, "take up your cross, and follow me".