“Observe the month of Abib, and keep the Passover to the Lord your God, for in the month of Abib the Lord your God brought you out of Egypt by night” (Deuteronomy 16:1 NKJV).

The month of Abib was the month that the Lord had delivered Israel from slavery in Egypt. It was therefore to be counted as the first month of the Hebrew year. Since the religious celebrations given by Moses were linked to certain times of the year, it became the role of the priests to certify the beginning of each new month based on the lunar cycle. The word “month” and “moon” are cognates in both the Hebrew and English language, and since the lunar cycle is 29.5 days, announcing the start of a new month was both science and art.
The word “Abib” means “fresh heads of grain,” or “green ears,” referring to the time of the year when crops of grain begin to come to a head. Today’s Jewish calendar no longer uses the name “Abib,” using the name “Nisan” in its place, which has been in use since the time when the Jews were released from Babylonian captivity (see Esther 3:7). The month of Abib corresponds to our months of March/April. Since the Jewish calendar is based on the lunar cycle and our calendar is based on the solar cycle, the date for Passover varies each year, and with it, the date for Easter does as well.
Passover was to be always celebrated in the month of Abib to remind Israel how the Lord had “passed-over” the homes whose doors were covered with the blood of the Passover lamb. This foreshadowed Jesus, the Lamb of God, who was given for the sins of the world.
So, the timing of the celebration for Jewish Passover and Christian Easter are linked. And their dates continue to move around in our modern calendar. This explains the 35-day span where Easter can occur (March 22 – April 25, inclusive).
It was in the month of Abib, meaning “new heads of grain,” that Jesus fulfilled His saying, “The hour has come that the Son of Man should be glorified. Most assuredly, I say to you, unless a grain of wheat falls into the ground and dies, it remains alone; but if it dies, it produces much grain” (John 12:23-24).