It has been much disputed whether this meal was a Passover, as apparently assumed by the synoptists, or some sort of solemn fellowship meal (Paul's word, ‘koinonia’ in Cor. 10: 16 can be translated ‘sharing’ or ‘fellowship’ or ‘communion’) which was being celebrated before the Passover. The gospel of John puts the death of Jesus at the time when the Passover lambs were being slaughtered in preparation for the meal (John 19: 14, 31).
Unfortunately there is a problem about the text in the account given by Luke: 22: 19b–20, which records Jesus' instruction to continue the rite, with the cup as the symbol of the new covenant: the verses are absent in certain Greek MSS. They are therefore omitted by REB; it is thought they were mistakenly introduced by an early copyist who recollected 1 Cor. 11: 25. On the other hand, these words are included by NRSV and NJB, probably on the assumption that it is out of character for those MSS which have the shorter version, since they are normally given to expansion rather than omissions. Luke regards the meal as a Passover on either text. If the longer text is correct, then we have a tradition in the synoptists and Paul (there is no mention of these words in John's account of the Supper) of the meal being a Passover, now given new significance by Jesus to explain the meaning of his crucifixion on the Friday. The facts that the meal was held in Jerusalem, at night, with a group of ‘at least ten’ as the requirement went, and Luke's mention of a second cup, all give support to the view that the meal was indeed a Passover. In that case, John has made a theological point by transferring the date in order that Jesus could be shown to be the true Passover lamb by dying at the hour of slaughter in the Temple. One tentative suggestion to reconcile the two dates is that the Last Supper was held on the Tuesday in accordance with the calendar of the sectarian book of Jubilees, whereas according to the official calendar the Passover meal was held on the Friday evening, shortly after the crucifixion.
The celebration of the Lord's Supper, or Eucharist (‘thanksgiving’) was at first attached to a common meal, at which there were some irregularities (1 Cor. 11). Social differences were exaggerated rather than diminished. So Paul argues that insensitivity to other members of the Body was a violation of the new covenant effected through Christ's death. The Lord's Supper must be a real bonding not an occasion of division (1 Cor. 10: 17).