Note 1 at Lk. 22:7: Matthew, Mark, and John all make a point of saying that these events took place on the first day of the feast of unleavened bread. Luke adds the additional statement that this was the day when the passover lamb must be killed. Matthew's and Mark's accounts go on to say that it was that evening when Jesus ate the passover meal with His disciples (Mt. 26:20; Mk. 14:17).

This looks like it contradicts John 18:28, which speaks of the Jews preparing to eat the passover after they delivered Jesus to Pilate the next morning. John 19:14 further complicates things by saying that the sixth hour on the day of Jesus' crucifixion was the preparation of the passover, implying that it was the next day when the passover was actually eaten.

All of this can be harmonized by remembering that the Jewish day did not begin at midnight as we are accustomed to. The Jewish day ran from sundown of one day to sundown of the next. Therefore, when Matthew 26:17, Mark 14:12, and Luke 22:7 speak of the first day of unleavened bread arriving and so the passover must be killed, they are speaking of the evening before the actual death of the passover lamb.

Jesus and His disciples ate the passover meal (see note 2 at Lk. 22:15, p. 414) in the evening of the 13th of the month of Abib or Nisan, one day early. This was because when everyone else was eating of the passover lamb the next evening, Jesus would have already offered Himself as our passover lamb and He would be in the grave. That same night Jesus was arrested in the garden (Mt. 26:57; Mk. 14:46; Lk. 22:54; Jn. 18:12) and brought before the high priests the next morning which was still the same Jewish day. This was the day that Luke states here "when the passover lamb must be killed."

John 19:14 calls this day the preparation of the passover because the actual passover meal was not eaten until that evening, which, according to Jewish reckoning, was the 14th day of the month of Abib or Nisan (Ex. 12:18; 13:4; Neh. 2:1; Est. 3:7).

In the Old Testament, there were allowances made for those who could not eat of the passover meal on the 14th day of the first month to eat this meal in the second month on the 14th day (Num. 9:2-14). Therefore, it is certainly understandable that our Lord, who was our passover Lamb (1 Cor. 5:7), could eat the passover meal with His disciples one day early.