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Jewish days begin after sunset (approx 6pm) in the evening.
The Passover began towards the end of the fourteenth day of the first month.
Leviticus 23:5 In the fourteenth day of the first month at even is the LORD’S passover. 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.
The first month was originally called Abib - Meaning: ‘an ear of corn’.
Deuteronomy 16:1 Observe the month of Abib, and keep the passover unto the LORD thy God: for in the month of Abib the LORD thy God brought thee forth out of Egypt by night.
The name of the month was changed to Nisan - Meaning: ‘their flight’ - after the Babylonian Captivity (Neh. 2:1).
It falls somewhere within our months of March and April. It changes in relation to our months because the Jews use a lunar calendar (months of 29 or 30 days), with an extra month inserted in the year periodically to maintain the seasons.
The Passover lamb was to be slain in the evening of the fourteenth day just prior to the beginning of the fifteenth day after sunset.
Exodus 12:6 And ye shall keep it up until the fourteenth day of the same month: and the whole assembly of the congregation of Israel shall kill it in the evening. 7 And they shall take of the blood, and strike it on the two side posts and on the upper door post of the houses, wherein they shall eat it. 8 And they shall eat the flesh in that night, roast with fire, and unleavened bread; and with bitter herbs they shall eat it.
The Hebrew translated ‘in the evening’ is the same as that translated as ‘at even’.
Exodus 38:39 The one lamb thou shalt offer in the morning; and the other lamb thou shalt offer at even:
This is understood to mean between approx 3pm and sunset.
This year the 14th of Abib/Nisan began after sunset on Sunday 17th of April.
In the year that Jesus was crucified the 14th of Abib/Nisan began after sunset on Wednesday. Jesus ate the Passover with his disciples on Thursday at sunset.
Luke 22:7 Then came the day of unleavened bread, when the passover must be killed. 8 And he sent Peter and John, saying, Go and prepare us the passover, that we may eat...11 And ye shall say unto the goodman of the house, The Master saith unto thee, Where is the guestchamber, where I shall eat the passover with my disciples?... 13 And they went, and found as he had said unto them: and they made ready the passover.14 And when the hour was come, he sat down, and the twelve apostles with him. 15 And he said unto them, With desire I have desired to eat this passover with you before I suffer:
It is likely that the original Passover fell on the same day of the week (working back from Exodus 16:1, and the lack of manna on the Sabbath in Exodus 16:22,23) but I currently believe that there is insufficient information given in scripture to be certain.
I hope you have found this helpful.
God bless you,