"You must take a pure unblemished animal, a one year old male from the sheep or the goats. Hold it in safekeeping until the afternoon of the fourteenth day of the month." (Ex. 12:5-6)

"…a pure unblemished animal…" The goal of a Jew is to continually present oneself before the master of the world like a pure innocent sheep, through perfect and undiluted divine service and absolute faith. The astrological sign of Aries-Ram is predominant in the month of Nissan

Why was the Passover Offering particularly on the fourteenth of the month, and why was it slaughtered only in the afternoon? The divine symbol of Egypt is the sheep. The astrological sign of Aries-Ram is predominant in the month of Nissan. (Zohar, parashat Pinchas 231a) In the middle of the month when the moon is full, the predominance of Aries is at peak. The afternoon hours of the day, when the light begins to give way to darkness is a time of the re-emergence of the forces of the Sitra Achra and the Yetzer Hara.

Therefore, G‑d commanded us to slaughter the sign of Egyptian divinity for our Passover Offering on the fourteenth of the month, when its rule is at its peak! This is another demonstration to Egypt and to the rest of the world, that G‑d alone is the the Master of the Universe.

[Based on Avodat Yisrael, parashat HaChodesh in parashat Vayikra; first published in B'Ohel Hatzadikim, Hachodesh 5759; http://www.nishmas.org/htmldocs/archtabl.htm]