⍟ Because Jesus’ rose from the dead, all who belong to him will be resurrected too.
Westminster Shorter Catechism:
Q. 38. What benefits do believers receive from Christ at the resurrection? A. At the resurrection, believers being raised up in glory, shall be openly acknowledged and acquitted in the day of judgment, and made perfectly blessed in the full enjoying of God to all eternity.
So one reason Christians celebrate the resurrection that has happened is because of the resurrection that will happen.