Today is Sunday. To the early Christians every Sunday was a celebration of the resurrection. On Sunday they would not kneel, and prayers were said with hands raised, which was the position of the cross to the early Christians. (Different way of looking at hand-raising, isn’t it?)
Jesus’ death was celebrated once a year, on Passover.
We’ve made a pretty big change in modern times. For many Christians, Sunday is a day on which we hear a sermon about Jesus’ death, while his resurrection is celebrated once a year on Easter.
Easter is a replacement for Passover. When the Council of Nicea ordered that Passover would only be celebrated on Sunday for Christians, it slowly became a celebration of the resurrection rather than a celebration of Jesus as the Passover Lamb.
Note that the Council of Nicea only changed the day for celebrating Passover, an annual occurrence. The weekly meeting for Christians had been primarily Sunday among Gentile Christians from the beginning.
In the fourth century, and since the second century for churches in the western Roman empire, Passover had been celebrated on the Sunday nearest Nisan 14, the day on which the Jews celebrate Passover. Over time, however, due to reasons not worth explaining here, it became the first Sunday after the first full moon on or after March 21. In the east, among the Eastern Orthodox Churches, April 3 is used rather than March 21. Yes, they often celebrate Easter on a different date.
The result is that things are a bit backwards today. Because we have also replaced the Gospel—which to the apostles was a proclamation of the entire life of Christ—with an outline of the atonement, our Sunday sermons often focus on the death of Christ. Thus, the weekly meeting now primarily focuses on Christ’s death, while his resurrection is celebrated annually on Easter.