Easter Sunday is, of course, the pivotal and most triumphant day in the calendar of the Christian Church. Interestingly however, no trace of an Easter celebration as we know it exists in the New Testament.
The celebration of Easter actually began with the early Jewish Christians who continued to celebrate the Passover, regarding Christ as the true Paschal Lamb. The original and prophetic sacrificial lamb had been the one eaten by Hebrew families their last night in captivity in Egypt.
An examination of rabbinic evidence from those days suggests that the paschal lamb, which had to be a perfect specimen, was arranged in the form of a cross before roasting. One spit went through the lower parts up to the head, and another across the back, to which the legs were attached. Furthermore, none of the bones were to be broken.
Sound familiar? To see the remarkable resonance here, compare the reading in Exodus 12:46b (“Do not break any of the bones”) with that from John 19:31-33:
“Now it was the day of Preparation, and the next day was to be a special Sabbath. Because the Jewish leaders did not want the bodies left on the crosses during the Sabbath, they asked Pilate to have the legs broken and the bodies taken down. The soldiers therefore came and broke the legs of the first man who had been crucified with Jesus, and then those of the other. But when they came to Jesus and found that he was already dead, they did not break his legs.”
For early Christians then, the Passover event naturally passed over into a commemoration of the death and resurrection of Jesus.
You can read an excellent related story by Rabbi Evan Moffic here: How Lent started with Passover.