Musar zu Bereschit 46:34

The zodiac sign of the lamb is the first of the twelve zodiac signs and represents the senior power to which G–d delegated a variety of such functions. It was this symbol which had to be slaughtered to drive home the point that without the consent of G–d it represented impotence instead of power. Since the Egyptians had made it a symbol of their שר, counterpart in the Celestial Regions, it had to be slaughtered by the Jews. For the same reason it was important that the redemption take place in the month of the ascendancy of that sign, and on the day that symbolised the zenith of its orbit, i.e. its power at its supposedly strongest. The Torah's explanation in Genesis 46,34, that any shepherd was an abomination to the Egyptians is logical. The mere suggestion that sheep needed human guardians -when they were viewed as a supreme deity- is an insult to their religion. When G–d said: החודש הזה לכם, "This month is for you," it is an announcement that Israel would be redeemed during the month of Nissan. G–d commanded that the lamb be taken in order to slaughter it and to humiliate by this single act the entire system upon which the Egyptians had built their position in this world. G–d performed judgments on the sheep, on the Egyptian deities, to demonstrate that He is not only a deity (like others, i.e. אלוקים) but that He is י-ה-ו-ה.