Deuteronomy 16:1

As a further preservative against idolatry, Moses proceeds to inculcate upon them a strict regard to the most exact observance of the three great annual festivals, appointed by their law to be celebrated at the stated place of national worship, these being designed for this very end, to keep the people steady to the profession and practice of the religion of the one true God. The first of these feasts was the passover, with that of unleavened bread; comprehending the sacrifice of the paschal lamb, with other sacrifices and oblations prescribed for each day of that whole week during which it was to continue. Of which see on Exodus 12:13. Observe the month of Abib Or of new fruits, which answers to part of our March and April, and was, by a special order from God, made the beginning of their year, in remembrance of their deliverance out of Egypt. By night In the night Pharaoh was forced to give them leave to depart, and accordingly they made preparation for their departure, and in the morning they perfected the work.