The Catechism in Questions & Answers

710. What is the significance of Easter?

The basis of this feast is the fact that Jesus Christ resurrected from the dead.
The resurrection of Jesus Christ took place on the first day of the week, namely on Sunday. Later, a specific Sunday in the course of the year was set aside for the celebration of Easter. With His resurrection, Jesus Christ demonstrated that He has also broken the power of death. The resurrection of Jesus Christ from the dead is also the basis of our belief in the resurrection of the dead, and the foundation of our hope in eternal life.

Resurrection of Christ: see Questions 184., 535. Resurrection of the dead: see Questions 92., 186., 535., 579.