The Feast of Unleavened Bread was instituted at the same time with the Feast of the Passover (Exodus 12:15-17), and from the beginning the two festivals were practically but one festival, never separated, though separable in idea. The Passover, strictly so called, lasted but one day, Nisan 14; the Feast of Unleavened Bread lasted seven days, Nisan 15-21. The whole made a festival of eight days, called indifferently the Feast of the Passover, or the Feast of Unleavened Bread. The bread to be eaten throughout the festival was unleavened, in order to remind the Israelites of the historical fact that on account of the urgency of the Egyptians, "the people took their dough before it was leavened, their kneading troughs being bound up in their clothes upon their shoulders" (Exodus 12:34), and quitted the land of their affliction in haste. Accordingly, in the Book of Deuteronomy it is appointed, "Seven days shalt thou eat unleavened bread therewith, even the bread of affliction; for thou camest forth out of the land of Egypt in haste: that thou mayest remember the day when thou earnest forth out of the laud of Egypt all the days of thy life" (Deuteronomy 16:3).
The first and the last day were to be days of holy convocation, on which no servile work might be done. It was on the first day, Nisan 15, that our Lord was crucified. The Pharisees found nothing in the holiness of the day to prevent their taking virtual part in his seizure and condemnation and death; but we are told by St. John that "they themselves went not into the judgment hall, lest they should be defiled, but that they might eat the Passover" (John 18:28). What is meant in this passage by "the Passover" is not the Paschal lamb which had already been consumed, but probably the peace offering, or chagigah, which had to be offered and eaten on the first day of Unleavened Bread. The public sacrifices on each of the seven days of the week were two young bullocks, one ram, and seven Iambs for a burnt offering, with the accompanying meat offerings, and one goat for a sin offering (Numbers 28:19-24). And these were followed by peace offerings made at the discretion of individuals, "according to the blessing of the Lord which he had given them" (Deuteronomy 16:17).