We know that in the first century it was common to refer to the entire 8-day festival as both “Unleavened Bread” and the “Passover.” Matthew, Mark, and Luke seem to prefer the designation “Unleavened Bread” for this entire festival period:
Mark 14:12: On the first day of Unleavened Bread, when the Passover Lamb was sacrificed…
Matthew 26:17: Now on the first day of Unleavened Bread the disciples came to Jesus to say 'Where do you want us to make the preparations for you to eat the Passover?
Luke 22:7: The day of Unleavened Bread came round, on which the Passover had to be sacrificed… (also see Acts 12:3 and 20:6).
John, on the other hand NEVER refers to the feast as “Unleavened Bread”. He ONLY uses the designation “Passover” (see John 2:13, 23; 4:45; 6:4; 11:55 x 2; 12:1; 13:1 18:28, 39; 19:14). That John only uses the word “Passover” for the entire weeklong celebration is clear in 19:14 which is poorly translated in the New Jerusalem. The literal Greek of this passage reads: And it was Preparation [Day] of the Passover, hour about the sixth and he says to the Jews, ‘Behold your king.’ The reference is to Preparation Day for the Sabbath that fell during the Passover festival. This is clearly the interpretation as we see in verse 31 as John continues: It was the Day of Preparation, and to avoid the bodies remaining on the Cross during the Sabbath…" [Greek = The therefore Jews that might not remain on the cross the bodies on the Sabbath because preparation it was for was great day that Sabbath …). The 1st century historian/Jewish priest Josephus recounts in both Antiquities of the Jews and The Jewish War that it was common to refer to the entire weeklong feast as both “Passover” and “Unleavened Bread”. John uses the term “Passover” for the entire 8-day festival.
2. John has already designated Thursday as the day the Passover lambs were sacrificed in John 12:1 when he records that the day before Palm Sunday it was 6 days until the feast of the Passover. As the ancients counted [no 0 place value at this time so the first in the series is designated #1] the 6th day from Saturday at Bethany [Sunday was Palm or Passion Sunday] would be Thursday which agrees with the Synoptic accounts (day 1= Saturday, day 2=Sunday, day 3=Monday, day 4=Tuesday, day 5=Wednesday, day 6=Thursday).
3. The reference in John 18:28: They did not go into the Praetorium themselves to avoid becoming defiled and unable to eat the Passover cannot be referring to the Passover supper that took place after sundown and was, therefore, in Jewish time the next day = Nisan 15. Ritual defilement in association with eating a sacrificial meal only lasted until sundown: Anything that an unclean person touches will be unclean, and anyone who touches it will be unclean until evening (Numbers 19:17-22). Also see the Mishnah: Ohalot, 18:7B, 18:10 which demonstrates that the dwelling places of Gentiles, but not their open courtyards, were considered unclean.
If this incident had taken place the morning of the Passover sacrifice, the Jews would have become ritually defiled by entering the abode of Gentiles (see Acts 11:2), but they had all day to become purified and by that night they would be able to eat the feast (see Numbers 28:16-25; Acts 10:28; and Leviticus chapter 22). Holiness in consuming sacred food: Anyone who touches anything made unclean by a dead body, or who has a seminal discharge, or who is made unclean by touching any kind of reptile or any one who has contaminated him with his own uncleanness, be it what it may, in short, anyone who has had any such contact will be unclean until evening, and must no eat holy things until he has washed his body. At sunset he will be clean and may then eat holy things, for these are his food (Lev 22: 4-7).
