The first month of Abib in the biblical calendar is based on observing when the barley ripens in Jerusalem. Every two or three years out of seven, needs an extra month added to keep the first month accurate with the spring season. Not based on a mathematical formula or the equinox, the timing of Abib can be difficult to predict. By making the timing for his holy days difficult to determine, God made sure the leaders couldn’t take the first season of unleavened bread for granted. If they became complacent, their entire year of holy day festivals could be out of time to the seasons. They had to stay vigilant and watch as the new grain started to ripen.

Exodus 13:9-10 Easy-to-Read Version
9 “This festival will help you remember; it will be like a string tied on your hand. It will be like a sign before your eyes. This festival will help you remember the Lord’s teachings. It will help you remember that the Lord used his great power to take you out of Egypt. 10 So remember this festival every year at the right time.

At Mount Sinai God gave the ten commandments to the Israelites. It was at this time he introduced them to his three main holy day seasons. The first, Passover and Unleavened Bread was when they left Egypt at the beginning of spring. The second was kept during the spring harvest of the early fruits, grains and produce. The third season was for the larger fall harvest, when the majority of their food was harvested.

Exodus 23:14-17 Common English Bible
14 You should observe a festival for me three times a year. 15 Observe the Festival of Unleavened Bread, as I commanded you. Eat unleavened bread for seven days at the appointed time in the month of Abib, because it was in that month that you came out of Egypt. No one should appear before me empty-handed. 16 Observe the Harvest Festival for the early produce of your crops that you planted in the field, and the Gathering Festival at the end of the year, when you gather your crop of fruit from the field. 17 All your males should appear three times a year before the Lord God.

These three festival seasons outline God’s plan for mankind’s salvation. Jesus shed his blood for all mankind, just as the Passover lamb’s blood saved the Israelites from death. Unleavened bread demonstrates how sin invades our lives completely, like leaven affects an entire lump of dough. The Holy Spirit arriving during the Feast of Weeks signalled the smaller first harvest of people, called to Jesus by God, had begun. These first two Holy Day seasons are commemorative. The return of Jesus, binding of Satan, the resurrection and salvation of those who never learned of Jesus, and God dwelling with man, are encompassed in the third upcoming fall season of holy days. Do we need to accept Jesus to be saved? How does Jesus save those who died before he came, or those who never knew him.