In the Bible, there are three "feasts". Each of those feasts contain certain days that are "sabbaths".
When one of those sabbaths occurs on the weekly 7th day sabbath (saturday), then that day is called a "high sabbath".
(just like sometimes your birthday occurs on a saturday).
There are several reasons why this particular day (15th of Nisan/Abib) was significant enough to be mentioned, the primary reason was to identify certain prophecies that were fullfilled that day.
Also, there are some folk who foolishly propose that Christ was crucified on a week-day other than Friday -- and John 19:31 provides a simple and adequate refute to those false prophets.
Notice:
Exodus 12 - Israel freed from bondage:
14 Nisan - The Lord's Passover
Night - Unleaven Bread first eaten.
Day - Passover lamb slain about 3pm, blood put on the door posts and lintel.
15 Nisan - 1st Day of Festival of Unleavened Bread - A Sabbath day
Night - Passover lamb eaten - Death Angel slays the firstborn of Egypt at midnight.
Day - Israel set free in the morning.
The reference in John 18:28 to the Passover meal being observed on the day AFTER the crucifixion is speaking of the meal in which the Passover lamb would be eaten, which would occur at the early hours of [Friday night] 15 Nisan, the Paschal lamb - symbolic of Jesus having been slain a few hours earlier on the [Friday] afternoon of the 14th. As a result, Matthew 26:17, Mark 14:12, and Luke 22:1, 7-8 all are actually referring to the 14th of Nisan (in a general sense) calling it the first day of unleavened bread.
Summary: Jesus was crucified late on 14 Nisan, the Lord's Passover.
Here is a chronological listing of the events of: the last supper, Gethsemane, arrest and trial of Jesus, the crucifixion, the weekly seventh-day Sabbath, and the resurrection - that puts all the pieces of the puzzle together in a way that satisfies all the Biblical accounts -- with NO CONTRADICTIONS.
14 Nisan/Abib - Friday (Beginning our Thursday night - The Lord's Passover).
Luke 22:7 Then came the day of unleavened bread, when the passover must be killed.
Luke 22:8 And he sent Peter and John, saying, Go and prepare us the passover, that we may eat.
Preparation for the Passover - Mat 26:17-19, Mark 14:12-16, Luke 22:7-13. -- Lev 23:5 In the fourteenth day of the first month at even is the Lord's passover. --- The 14th of Nisan is to be the Lord's Passover, and it was just after sunset (Thursday night - the beginning of the 14th day) that the Passover meal of unleavened bread was celebrated by Jesus with His disciples.
Judas identified as the betrayer- Mat 26:21-25, Mark 14:18-21, Luke 22:21-23, John 13:21-30.
The Lord's Supper- Mat 26:26-29, Mark 14:22-25, Luke 22:14-16.
Jesus retires to Gethsemane and is arrested- Mat 26:30-56, Mark 14:26-52, Luke 22:39-53, John 18:1-12.
In the morning of Friday (but still 14 Nisan) the trials took place, (Matt. 26:57-27:26 Mark 14:53-15:15, Luke 22:54-23:25, John 18:13-19:16), and the crucifixion began at about 9am (the third hour- Mark 15:25).
Jesus died at the very moment the Passover lamb was to be slain at the Temple, the ninth hour (our 3pm) on the 14th of Nisan (our Friday). From the moment Jesus was laid in the tomb, UNTIL sunset, the Jews reckoned to be the first day in the grave, even though it was only a few hours.
All of this took place on what was the preparation day - preparation not only for the 7th day Sabbath, but also for the upcoming Feast of Unleavened Bread.
Note - that particular seventh day Sabbath was a "high" day ... John 19:31 The Jews therefore, because it was the preparation, that the bodies should not remain upon the cross on the sabbath day, (for that sabbath day was an high day,) besought Pilate that their legs might be broken, and that they might be taken away.
15th of Nisan/Abib - Saturday (A double "high" Sabbath day which began at sunset on our Friday night. First day of the week long Festival of Unleavened Bread). ... it was a "high" Seventh day (Saturday) Sabbath because it was ALSO the 15th of Nisan/Abib, a feast day Sabbath.
Lev 23:6 And on the fifteenth day of the same month is the feast of unleavened bread unto the LORD: seven days ye must eat unleavened bread. Lev 23:7 In the first day ye shall have an holy convocation: ye shall do no servile work therein.
The Messiah rests in the tomb, observing the Sabbath day rest the entire day. This is the second day in the grave.
16th of Nisan/Abib (The day of first fruits, Resurrection day) - Sunday, which began at sunset - on our Saturday night.
Not a Sabbath day in type or antitype.
The resurrection takes place at some time after the beginning of the day (at sunset Saturday) but before the [Sunday] morning sunrise. Just exactly when after sunset the resurrection took place is uncertain, but that it happened on what we today call Sunday is really quite clear as Luke 24 showed.
But here is more evidence: 1 Cor 15:20 But now is Christ risen from the dead, and become the Firstfruits of them that slept.
So just how does the following verse relate? -- Lev 23:10 Speak unto the children of Israel, and say unto them, When ye be come into the land which I give unto you, and shall reap the harvest thereof, then ye shall bring a sheaf of the Firstfruits of your harvest unto the priest: Lev 23:11 And he shall wave the sheaf before the LORD, to be accepted for you: on the morrow after the sabbath the priest shall wave it.
The wave sheaf of Barley represented the first fruits of the resurrection, the Messiah (1 Cor 15:20), and the day it was presented was the day AFTER the Sabbath as Lev 23:11 just proved. (The Sabbath meant here is 15 Nisan/Abib, the first day of Unleavened Bread [Lev 23:6-7] - not necessarily "Saturday", however this year that calandar date did indeed fall on that particular weekly day.
Clearly then, since the first day of Unleavened Bread coincided with the Seventh day Sabbath that specific year, the resurrection of Jesus (the first fruits), happened on 16 Nisan/Abib the day AFTER the "double" or "high" Sabbath, on the first day of the week, Sunday.
Because the Firstfruits represents the resurrection, the day of Firstfruits must clearly occur on the third day after the crucifixion (14 Nisan), to fulfill scripture.
PS- if you would like more info on this, feel free to send me a private email.