Albert Barnes Commentary Exodus 12:2

"This month shall be unto you the beginning of months: it shall be the first month of the year to you." — Exodus 12:2 (ASV)

This month - Abib (Exodus 13:4). It was called “Nisan” by the later Hebrews, and nearly corresponds to our April. The Israelites are directed to take Abib from now on as the beginning of the year; the year previously began with the month Tisri, when the harvest was gathered in; see (Exodus 23:16). The injunction concerning Abib or Nisan referred only to religious rites; in other affairs they retained the old arrangement, even in the beginning of the Sabbatic year; see (Leviticus 25:9).