Passover, like all other Jewish holidays, is set according to a lunar calendar and falls on the 14th day of the month of Nissan. In the first two centuries, churches in Asia Minor (modern Turkey) followed the practice of Jewish Christians and commemorated the death and resurrection of Jesus on Nissan 14, no matter on what day of the week it happened to fall. (The name "Easter" was not yet given to the holiday. Rather, it was called pascha, Greek for Passover.) But sometime in the middle of the second century, some non-Jewish Christians began celebrating it on the Sunday following Nisan 14.
What resulted was a controversy over the date of the observance. In A.D. 197 Victor, Bishop of Rome, excommunicated Christians who observed pascha on Nisan 14. But it was the Emperor Constantine who permanently settled the debate in the fourth century, when he officially required all churches to observe pascha on the Sunday after Nissan 14.
But why change the date? What was wrong with celebrating the 14th of Nisan? That brings us to the culture of the early church. After the first century or so, the church became predominantly non-Jewish. Sadly, along with this shift came an increasingly anti-Semitic tendency, reflected in the theological writings of many leaders of the first church. In these writings the Jewish people were frequently depicted as wicked and abandoned by God, and all the blessings given to the Jewish people by God were appropriated by the Church for itself. In an anti-Judaic culture, the desire to celebrate pascha at a different date than the Jewish Passover gradually won out. When this final separation of pascha from Passover occurred, the day became focused on the Resurrection alone, rather than on the entire sequence of death and resurrection together.
From about the seventh century on, for various calendrical reasons, the date of what was by then called Easter was further modified. Today Easter (or as some prefer to call it, Resurrection Sunday) is aligned with the solar calendar. It falls on the first Sunday after the first full moon that follows the vernal equinox. Because of various technicalities, Easter falls on a different date for Eastern Orthodox Christians than for Western Christians. In the calendar used by the western Churches, Easter can fall anywhere from March 22 to April 25th. Because of the divergences between the solar and lunar calendars, Passover and Easter fall at a variety of times in relation to one another.
Read more about the Holiday Of Passover.
Rich Robinson with Jews for Jesus.