It’s likely the case that John’s original audience saw no contradiction between John’s Last Supper chronology and the chronology of the other Gospels because they understood the way terms were used interchangeably in their day. Unfortunately, for modern readers who are unaware of the context, John’s language can sometimes be misunderstood to represent a different chronology than the Synoptics.
Close readers of the Gospels understand that John’s timeline of the Last Supper seems to differ from the Synoptic Gospels (Matthew, Mark, and Luke). The Synoptics indicate that the disciples prepared the Passover meal “on the first day of Unleavened Bread,” or Thursday night (Mark 14:12; see also Matt. 26:17; Luke 22:7). Judas went out to betray Him that evening, and Jesus was arrested in the night. He was then crucified on Friday. He was in the grave until Sunday morning, on which day He was raised from the dead.
Yet John says this after the Last Supper had occurred, when the Jews went to Pilate’s headquarters: “They themselves did not enter the governor’s headquarters, so that they would not be defiled, but could eat the Passover” (John 18:28). He then later says, after Jesus was crucified, that “it was the day of Preparation of the Passover” (John 19:14). This means that Jesus’ arrest and trial would have happened before Passover, unlike in the Synoptics, where Jesus’ arrest and trial happened after Passover.
Is this a contradiction? It seems that way on first reading. Various solutions have been offered to resolve this seeming contradiction. Some have argued that Jesus celebrated the Passover according to a different calendar in use at this time, such as according to a special Pharisaic calendar. Yet there is little evidence in the Gospels or historical records to validate such a view. Others have argued that Jesus wasn’t celebrating a Passover meal, but rather a different but related festival meal. The trouble with this argument is that one is left with the opposite problem—John’s chronology makes sense, but the Synoptics’ chronology doesn’t. The plain meaning of the synoptic Gospels indicates that Jesus was celebrating the Passover meal.
There is a final view that seems most biblically justified and understandable to me, but it requires some explanation. The first thing to understand is that Passover was simply a meal that began on the first day of the Feast of Unleavened Bread, which went for several days. Western Christians don’t often celebrate multiday holidays, but many in other cultures do. The Feast of Unleavened Bread was a week-long feast. It was one of several national celebrations for the Jews. It reminded them of their liberation from Egypt and God’s preservation of His people in the wilderness years. Passover kicked it all off, just like the original Passover kicked off Israel’s liberation from Egypt and led to the wilderness years and the promised land.