Mark 14 tells of Jesus eating the Passover with his disciples. But after the Last Supper and when Jesus is captured, John 18:28 mentions the priests "themselves did not enter into the Praetorium so that they would not be defiled, but might eat the Passover". Does this mean there were two Passovers?
The Passover celebration in Jesus’ day was a complicated affair lasting a full 24 hour period. Remember, days on the Jewish calendar are counted from evening to evening. During the first evening, families celebrated the passover in their homes by consuming a lamb slain earlier that afternoon. As the law required, that sacrifice could not remain in the morning but had to be completely consumed over that evening.
Ex. 12:6 ‘You shall keep it until the fourteenth day of the same month, then the whole assembly of the congregation of Israel is to kill it at twilight.
Ex. 12:7 ‘Moreover, they shall take some of the blood and put it on the two doorposts and on the lintel of the houses in which they eat it.
Ex. 12:8 ‘They shall eat the flesh that same night, roasted with fire, and they shall eat it with unleavened bread and bitter herbs.
Ex. 12:9 ‘Do not eat any of it raw or boiled at all with water, but rather roasted with fire, both its head and its legs along with its entrails.
Ex. 12:10 ‘And you shall not leave any of it over until morning, but whatever is left of it until morning, you shall burn with fire.
Ex. 12:11 ‘Now you shall eat it in this manner: with your loins girded, your sandals on your feet, and your staff in your hand; and you shall eat it in haste — it is the LORD’S Passover.
Deut. 16:1 “Observe the month of Abib and celebrate the Passover to the LORD your God, for in the month of Abib the LORD your God brought you out of Egypt by night.
Deut. 16:2 “You shall sacrifice the Passover to the LORD your God from the flock and the herd, in the place where the LORD chooses to establish His name.
Deut. 16:3 “You shall not eat leavened bread with it; seven days you shall eat with it unleavened bread, the bread of affliction (for you came out of the land of Egypt in haste), so that you may remember all the days of your life the day when you came out of the land of Egypt.
Deut. 16:4 “For seven days no leaven shall be seen with you in all your territory, and none of the flesh which you sacrifice on the evening of the first day shall remain overnight until morning.
Deut. 16:5 “You are not allowed to sacrifice the Passover in any of your towns which the LORD your God is giving you;
Deut. 16:6 but at the place where the LORD your God chooses to establish His name, you shall sacrifice the Passover in the evening at sunset, at the time that you came out of Egypt.
Deut. 16:7 “You shall cook and eat it in the place which the LORD your God chooses. In the morning you are to return to your tents.
The Passover meal was to be eaten on the first night of Passover in private homes by families. In Jesus’ day, the nation had adopted an additional ritual of a sacrificing a single lamb for the sake of the entire nation in the temple during the day of Passover following that first evening. In the week Jesus died, the Passover began on a Wednesday evening and concluded on a Thursday evening. So most Jews ate their meal Wednesday night according to Exodus and Deuteronomy, while the single, national sacrifice took place in the temple the following Thursday morning. That lamb became a meal for the priests and elders during that day prior to the end of Passover (and contrary to the Scripture).
So Israel celebrated one Passover celebration that stretched over a 24-hour period. Everyone ate one meal, with most eating it the night before as required by Scripture, but some religious leaders ate it on the following day following the national sacrificial lamb. This is why in John 18:28 the religious leaders were concerned about being defiled on the Thursday morning, because it would have disqualified them from participating in the national sacrifice and meal on that day.
In the gospels, we see Jesus following a similar pattern as the Lamb of God. He participated with His disciples in a Passover meal on the Wednesday night prior to His death (though there was no lamb present at His table because Jesus was the Lamb), and then the next morning Jesus hung on a cross as the Lamb of God for Israel and the world, even as the nation was sacrificing their national lamb at the temple.
For more information on this topic, please read:
What day of the week did Jesus die?
What date did Jesus dies?