Ezekiel was one of the captives who were carried with Jehoiachin in 597 B.C. to Babylonia, and was settled with many other exiles at a place called Tel-abib (iii.
Before the departure of the Israelites from Egypt their year commenced at the autumnal equinox; but in order to solemnize the memory of their deliverance, the month of Nisan or Abib, in which that event took place, and which falls about the time of the vernal equinox, was afterwards regarded as the beginning of the ecclesiastical or legal year.
The Israelites were commanded to select on the tenth of Abib (Nisan) a he-lamb of the first year, without blemish, to kill it on the eve of the fourteenth and to sprinkle with its blood the lintel and sidepost of the doors of their dwellings so that the Lord should "pass over" them when he went forth to slay the first-born of the Egyptians.
Observe the month of Abib and keep the Passover because in that month God brought out the Israelites from Egypt.
Thus in the Elohist and in Deuteronomy the date of the festival is only vaguely stated to be in the month of Abib, while in the Holiness Code and in the Priestly History the exact date is given.