During the first century, Christians did not believe that the official calendar of Rome, or the local calendars that honored the deities of various cities, marked real time. In their minds, the only time that mattered was eternity and the moment when God would dissolve this world in a final judgment that would bring his own people into Paradise. They were convinced that Jesus had been the first person to make this transition.
Baptism emerged as a key Christian ritual. Baptized Christians who had prepared themselves to follow Christ, after an extensive period of study, prayer and fasting, shared in his death and resurrection on Easter, the Sunday after Passover. They, too, would someday join him in Paradise.
The logic that joined Passover, baptism, and Jesus’ death and resurrection is a principle of the entire liturgical calendar of Christianity that endures to this day in the penitential season of Lent.