The Kingdom of God that Jesus taught about has significantly deepened, transforming even death itself. Jesus Christ is risen from the dead. The Resurrection of Jesus is not a return to this life. Lazarus, who was raised from the dead by Jesus, had to die once more. But Jesus moves beyond this life taking our humanity into the life of the Trinity itself. Jesus will never die again. We are invited into the same journey. "Whoever wishes to come after me must deny himself, take up his cross, and follow me." (Mark 8:34).
Although the Resurrection of Jesus is shrouded in mystery. No one was an eye-witness to the moment of the resurrection. But the resurrection is real and true (cf. Catechism of the Catholic Church 638-639). As St. Paul reminds us,
"For I delivered to you as of first importance what I also received, that Christ died for our sins in accordance with the scriptures, that he was buried, that he was raised on the third day in accordance with the scriptures, and that he appeared to Cephas, then to the twelve. Then he appeared to more than five hundred brethren at one time, most of whom are still alive, though some have fallen asleep. Then he appeared to James, then to all the apostles. Last of all, as to one untimely born, he appeared also to me." (1 Corinthians 15:3-8).
We continue to proclaim this truth each Sunday by our profession of faith: "On the third day he rose again in fulfillment of the Scriptures" (Nicene Creed).
Easter, the celebration of the Resurrection of the Lord, is the culmination of the life and death of Jesus. Therefore, Easter is the first of all the Christian feast days. Not just a one-day celebration, the fifty days of Easter from Easter Sunday to Pentecost is celebrated as one joyful feast (cf. Catechism of the Catholic Church 1169). Easter was the original feast of the early Church; it was the first feast to be observed annually by early Christians.