The postexilic name of the first Jewish lunar month of the sacred calendar, corresponding to part of March and part of April. (Ne 2:1; Es 3:7) This month, first called “Abib,” was originally considered the seventh month and is evidently the month referred to at Genesis 8:4. At the time of the Exodus from Egypt, Jehovah assigned this month to be “the first of the months of the year.” (Ex 12:2; 13:4; Nu 33:3) From then on, a distinction existed between a sacred calendar instituted by Jehovah and the previous secular calendar.—See CALENDAR; ABIB.
The weather was often quite cool during this spring month, and in Jerusalem, fires were lit at night to provide warmth. (Joh 18:18) Snow has even fallen in Jerusalem as late as April 6, as it did in 1949. Nisan came at about the close of the rainy season, and the latter or spring rains were counted on to bring the grain to fullness prior to the harvest. (De 11:14; Ho 6:3; Jer 5:24) At this time of the year the Jordan River was normally at flood stage. (Jos 3:15; 1Ch 12:15) The barley harvest began along the coastal plains, and down in the subtropical Jordan Valley the wheat was reaching maturity. (Ru 1:22; 2:23) About this time, harvested flax on Rahab’s rooftop in Jericho provided a place for the Israelite spies to hide.—Jos 2:6; 4:19.
Adjusting the Lunar Calendar. God’s command required that the Israelites offer up a sheaf of the firstfruits of their harvest on the 16th day of Nisan (Abib) and that, on the 50th day thereafter, they offer up a second grain offering. These offerings corresponded naturally with the barley and wheat harvests, respectively. This precept made essential an adjustment in the calendar of lunar months used by the Israelites. There was need to compensate for the difference of 11 1⁄4 days between the full solar year and the shorter lunar year. Otherwise, within the space of three years, the month of Nisan would arrive some 33 days earlier in the season and far ahead of the barley harvest. The Bible record does not specify what method was originally used by the Israelites to accomplish such coordination, but the evidence indicates that a 13th month was added every two or three years to restore the seasons to their proper position in the calendar year. It seems likely that this was determined by simple observation, relating the new moon to the vernal, or spring, equinox of the sun, which comes about March 21 of each year. If the new moon that would ordinarily mark the start of the month of Nisan (Abib) was too distant from the time of the spring equinox, then the month was counted as a 13th or intercalary month, and Nisan began with the following new moon. It was not until the fourth century C.E. that a definitely standardized calendar was adopted by the Jews.
The first of Nisan’s festivals was the Passover, originally celebrated in Egypt; it came on the 14th of the month and included the sacrifice of the paschal lamb. (Ex 12:2-14; Le 23:5; De 16:1) The following day was the beginning of the week-long Festival of Unfermented Cakes, running from the 15th to the 21st of the month. On the 16th of Nisan came the offering of the firstfruits of the barley harvest.—Ex 12:15-20; 23:15; 34:18; Le 23:6-11.
Lord’s Evening Meal Instituted. Over 15 centuries after the Exodus, on Nisan 14 of the year 33 C.E., Jesus gathered with his 12 apostles in Jerusalem to celebrate the last valid Passover, and then, having dismissed the traitorous Judas, he proceeded to institute the memorial of his death by means of the Lord’s Supper, or Evening Meal. (Mt 26:17-30; 1Co 11:23-25) Before Nisan 14 passed, he died as the Lamb of God. On Nisan 16, the day the priest at the temple waved the firstfruits of the barley harvest, Jesus, as the firstfruits of the resurrection, was raised up to life again.—Lu 23:54–24:7; 1Co 15:20.
In obedience to Christ’s instructions, “Keep doing this in remembrance of me,” the 14th day of Nisan continues to be observed by his followers till this day as the time for memorializing Christ’s death.—Lu 22:19, 20; see LORD’S EVENING MEAL.