John 19:42 and Luke 23:53 appear to contradict eating the night of the 15th if the preparation day is the 14th. Christ was already in the tomb.
John 19:42 There laid they Jesus therefore because of the Jews' preparation day; for the sepulchre was nigh at hand.
Luke 23:53 And he took it down, and wrapped it in linen, and laid it in a sepulchre that was hewn in stone, wherein never man before was laid. 54 And that day was the preparation, and the sabbath drew on.
Mark defines 'the preparation' for his readers:
Mar 15:42 And now when the even was come, because it was the preparation, that is, the day before the sabbath, [/B]
It is the Greek word 'paraskeue' and in every place in all four gospels where the word 'paraskeue/the preparation' is used, it is in reference to the day before the seventh day Sabbath.
Others will argue that Mark was referring to a sabbath other than the seventh day Sabbath. But, Mark was taking the time to inform us what the word 'paraskeue' means and if he was referring to something other than the seventh day Sabbath, he would have said so, otherwise his effort to inform us of the meaning is an exercise in futility.
In Greece today, the word for Friday is 'Paraskeve' which is derived from the Koine Greek 'paraskeue'.
I had the oportunity to meet an Egyptian Coptic Christian about a year ago. I asked him what the word Paraskeve meant to him and he replied, "It's the day before the seventh day Sabbath."
In the gospels, the word 'hetoimazo' is used in every case to describe the 'preparation' of the Passover meal on the 14th, not 'paraskeue'.
If one understands the plain statement of the text that the Lord Jesus ate the Passover meal at the appointed time with all Israel and one also understands the meaning of 'paraskeue', then everything falls into place and all four gospel accounts of the timeline harmonize.
If one does not understand these things then, Johns' account appears to contradict the other three.