I've never thought it particularly important to know when Easter is on each year - That is until I had to reschedule a lunch I had made with a non-Christian colleague on Good Friday and his reaction was "...but it should be an important date for you to remember."
So I want to ask the question: How attached should a Christian be to the date on which something symbolic occurs? In society many days are very important, like birthdays, anniversaries and when holidays begin (or end). Public Holidays are of particular significance to workers: Advance Australia Fair! (26th Jan); Lest we Forget (25th April), etc.
On top of those there are many religious holidays and even more so if the religion is works-based.
However as a Christian under the new covenant, there are no dates that have specifically been set for us in the New Testament to remember. We're simply called to maintain fellowship with each other as a church under God. The dates for things like Christmas and Easter came later (they are however still very good to celebrate). We've moved on from a law-based covenant where regulations like dates mattered, to a spirit-based covenant where it is our standing before God that matters.
"Therefore let no one pass judgment on you in questions of food and drink, or with regard to a festival or a new moon or a Sabbath. These are a shadow of the things to come, but the substance belongs to Christ...If with Christ you died to the elemental spirits of the world, why, as if you were still alive in the world, do you submit to regulations--'Do not handle, Do not taste, Do not touch'" Colossians 2:21
Many religions including the Old Testament place significant importance on regulations and the law. This includes many things from what one could eat, touch, or even when festivals should be celebrated, with strict punishments for those who do not follow these regulations. Colossians here reminds us that we ought not to be judged by the law or the regulations for the sake of regulation, but to submit to Christ who seeks our very lives.
Easter then, should be so much more significant than how the date is calculated. It's what we are remembering in that period that should be life-changing for us.
We are remembering that God is very angry with us. He's angry with us to the point of wrath because we have rejected him even though he is our Father and maker. More importantly he wants us to know he's willing to forgive us. He shows his commitment to our welfare by sending Jesus, his one and only Son, to die for us and to take the punishment we deserve. He validates it by raising Jesus back from the dead to show us that He can give us life again. Jesus dying on the cross changes our direction from living our life our own way to living our life His way because we owe it to him. We owe him our lives.
"Blessed be the God and Father of our Lord Jesus Christ! According to his great mercy, he has caused us to be born again to a living hope through the resurrection of Jesus Christ from the dead, to an inheritance that is imperishable, undefiled, and unfading, kept in heaven for you" 1 Peter 1:3-4
We have the Easter weekend to celebrate that God in his great mercy doesn't deliver his punishment upon us but gives us a new life that leads to an inheritance 'that is imperishable, undefiled and unfading, kept in heaven' for us. We have that hope only because we understand and believe that Jesus died and rose from the dead, knowing that without God's mercy our destiny is certain physical and spiritual death.
So when is Easter? It's the Friday to Monday, where the Sunday follows the paschal full moon. The paschal full moon was the set date for the Passover in the Jewish Calendar. This was also the day of Jesus' last supper with his disciples (Thursday). He was crucified the following day (Friday) and resurrected on the third day (Sunday).
Should we then, remember the date? Well maybe not the specific date months in advance, but you should know when it's coming so you can set it aside to spend with your brothers and sisters in Christ before God, because our lives now revolve around Him. It's also a great time to invite non-Christians so that they can be challenged with this message.
Note:
If you are particularly curious as to how it's calculated you can check out this website for a very historical and mathematical explanation.
http://www.assa.org.au/edm.html#Method